Abstract:
A color image reading apparatus includes a color separation unit to separate a color of an image of an object into more than three visible color wavelength components in a visible wavelength range and an image sensing unit to read the image of the object whose color is separated by the color separation unit and outputting image signals of the respective colors. The apparatus also has a color calculation circuit to calculate image data of not less than three colors from the image signals corresponding to the colors separated by said color separation unit.

Description:
[0001]    The entire disclosure of Japanese Patent Application No. 9-319608 including specifications, claims, drawings, and summaries is incorporated herein by reference in their entirety.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a color image reading apparatus.  
           [0004]    2. Related Background Art  
           [0005]    A color image reading apparatus for switching illumination light generally uses three light sources for emitting red (R), green (G), and blue (B) light components, respectively. The wavelength of illumination light is switched by sequentially switching the light source to be turned on.  
           [0006]    A color image is reproduced on the basis of R, G, and B image componentswhich have been read using an R, G, and B light sources, respectively.  
           [0007]    The conventional color image reading apparatus uses a fluorescent lamp or the like as a light source. Some recent apparatuses use a light-emitting diode as a light source.  
           [0008]    Recent light-emitting diodes are quite useful as illumination light sources because of high luminance. In addition, various light-emitting diodes having different emission wavelengths are available.  
           [0009]    When light-emitting diodes are used as light sources, three light-emitting diodes, i.e., a red light-emitting diode having a peak emission wavelength in the range longer than 600 [nm], a green light-emitting diode having a peak emission wavelength near 550 [nm], and a blue light-emitting diode having a peak emission wavelength in the range shorter than 500 [nm] are used.  
           [0010]    Popular color image reading apparatuses directly output the data of read R (red), G (green), and B (blue) color components. On the other hand, some color image reading apparatuses execute color correction calculation to improve color reproducibility. As the color correction calculation, for example, 3×3 matrix calculation is performed.  
           [0011]    The conventional color image reading apparatuses cannot obtain sufficient color reproduction performance when an image is read from an original such as a color reversal film with a wide color gamut. That is, the color image reading apparatuses fail to provide satisfactory color reproduction capability. Especially, when a film having four photosensitive layers is used as an original, the color development characteristics of the film are more complex than the color reproduction capability of the color image reading apparatus. For this reason, the color difference between the actual original image and the read image becomes more conspicuous.  
           [0012]    The color reproducibility is somewhat improved by executing color correction calculation. However, the color reproducibility is still poor. Especially, when a film having four photosensitive layers is used as an original, further improvement of color reproducibility is required.  
           [0013]    Color image reading apparatuses sequentially read images of the R, G, and B color components. This prolongs the image reading time as compared to monochrome reading.  
           [0014]    When the emission intensity of the illumination light source is low, the illuminance of the illuminated original surface is low. To read the image at a sufficient brightness, the exposure time (charging time) of the image sensing device must be made longer. As the exposure time becomes longer, the image reading time also becomes longer.  
         SUMMARY OF THE INVENTION  
         [0015]    It is an object of the present invention to improve the color reproducibility of a color image reading apparatus without largely increasing cost. It is another object of the present invention to provide a color image reading apparatus capable of shortening the image reading time.  
           [0016]    According to the present invention, there is provided a color image reading apparatus comprising:  
           [0017]    a color separation unit to separate a color of an image of an object into not less than four visible color wavelength components in a visible wavelength range;  
           [0018]    an image sensing unit to read the image of the object whose color is separated by the color separation unit and outputting image signals of the respective colors; and  
           [0019]    a color calculation circuit to calculate image data of not less than three colors from the image signals corresponding to the colors separated by the color separation unit.  
           [0020]    The color image reading apparatus according to one mode of the present invention has a light source having four or more types of light emitters which have different peak emission wavelengths in the visible light range, an illumination optical system for illuminating an original with light from the light source, an image forming optical system for forming the image of the original illuminated by the illumination optical system, a one-dimensional image sensing unit for reading the image formed by the image forming optical system as a one-dimensional image, a subscan unit for moving the position of the original relative to the one-dimensional image sensing unit in an axial direction crossing the axial direction of the one-dimensional image, an emission color switching unit for controlling the state of each of the four or more types of light emitters to switch the emission color of the light source, and color calculation means for obtaining three or more color-converted data on the basis of a plurality of color data obtained from the image sensing unit.  
           [0021]    In this apparatus, the light source for illuminating the original has four or more types of light emitters which have different peak emission wavelengths in the visible light range. The emission color switching device controls the state of each of the four or more types of light emitters to switch the emission color of the light source. The original is illuminated with light from the light source through the illumination light system. The image of the illuminated original is formed on the one-dimensional image sensing device by the image forming optical system. The one-dimensional image sensing device reads the image formed by the image forming optical system as a one-dimensional image. Since the subscan means moves the position of the original relative to the one-dimensional image sensing means in the axial direction crossing the axial direction of the one-dimensional image, the two-dimensional image of the original can be read.  
           [0022]    The color calculation means obtains three or more color-converted data on the basis of a plurality of color data obtained from the image sensing means. For example, when five types of light emitters of R (red), Y (yellow), G (green), C (cyan), and B (blue) are used, the image of each of the R, Y, G, C, and B color components can be sequentially read.  
           [0023]    To output color image data having three color components of R, G, and B, which are generally used, image data of three color components of R, G, and B are generated from image data of each of the color components of R, Y, G, C, and B by calculation (conversion) by the color calculation means. The color data of the image generated on the basis of the image data of four or more color components has good color reproducibility as compared to color data obtained by the conventional image reading apparatus. Therefore, even when a film having four photosensitive layers is used as an original, the color image reading apparatus of the present invention can reproduce the color of the original image more accurately.  
           [0024]    In this color image reading apparatus, the emission color switching means may have, as a reading mode, a first mode in which the emission color of the light source is sequentially switched to any one of three colors, and a second mode in which the emission color of the light source is sequentially switched to any one of N colors (N≧4). More preferably, the color calculation means automatically may switch the contents of formulas representing the correlation between the input color data of three or more colors and output color data of three or more colors in accordance with the reading mode of the emission color switching means.  
           [0025]    When images of four or more color components are to be sequentially read, in some cases, the reading time may become longer than that in reading images of three color components due to more complicated image processing etc. When a film having four photosensitive layers is used as an original, high color reproducibility is required for the color image reading apparatus. However, when the original has a relatively narrow color gamut, it is sometimes more preferable to shorten the reading time rather than to increase the color reproducibility. When the first mode in which the emission color of the light source is sequentially switched to any one of three colors and the second mode in which the emission color of the light source is sequentially switched to any one of N colors (N≧4), the color reproducibility is relatively low while the reading time is relatively short in the first mode. In the second mode, the color reproducibility is improved while the reading time becomes longer.  
           [0026]    The color components of input image data change between the first and second modes. The color calculation means automatically switches the contents of formulas representing the correlation between the input color data of three or more colors and output color data of three or more colors in accordance with the reading mode.  
           [0027]    In this color image reading apparatus, when the emission color switching means selects a specific color as the color to be emitted by the light source in a specific reading mode, a plurality of light emitters having different peak emission wavelengths may be simultaneously driven to emit light. For example, B (blue) and C (cyan) have a small wavelength difference. For this reason, B and C can be regarded as one color (B). In this case, when the B and C light emitters are simultaneously turned on, the emission intensity of the light source increases as compared to a case wherein only the B light emitter emits light. Similarly, G (green) and Y (yellow) have a small wavelength difference. For this reason, G and Y can be regarded as one color (G). In this case, when the G and Y light emitters are simultaneously turned on, the emission intensity of the light source increases as compared to a case wherein only the G light emitter emits light. As the emission intensity of the light source increases, the illuminance of the original increases. For this reason, even when the exposure time of the image sensing device is shortened, a bright image can be read. That is, the image reading time can be shortened. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]    [0028]FIG. 1 is a partially cutaway front view of an image reading apparatus;  
         [0029]    [0029]FIG. 2 is a longitudinal sectional view showing the light source unit of the image reading apparatus shown in FIG. 1;  
         [0030]    [0030]FIG. 3 is a plan view of the light source unit;  
         [0031]    [0031]FIG. 4 is a graph showing the characteristics of five light-emitting elements used in the light source unit;  
         [0032]    [0032]FIG. 5 is a perspective view showing the illumination unit of the image reading apparatus shown in FIG. 1;  
         [0033]    [0033]FIG. 6 is a schematic exploded view showing the optical path from the light source unit to a linear image sensor;  
         [0034]    [0034]FIG. 7 is a schematic exploded view showing the optical path from the light source unit to the linear image sensor;  
         [0035]    [0035]FIG. 8 is a block diagram showing the electrical circuit in the image reading apparatus 60 shown in FIG. 1;  
         [0036]    [0036]FIG. 9 is a flow chart showing operation of a main control unit shown in FIG. 8;  
         [0037]    [0037]FIG. 10 is a flow chart showing contents of step S 11  in FIG. 9;  
         [0038]    [0038]FIG. 11 is a flow chart showing contents of step S 12  in FIG. 9;  
         [0039]    [0039]FIG. 12 is a flow chart showing contents of step S 13  in FIG. 9;  
         [0040]    [0040]FIG. 13 is a flow chart showing contents of step S 14  in FIG. 9;  
         [0041]    [0041]FIG. 14 is a flow chart showing contents of step S 15  in FIG. 9; and  
         [0042]    [0042]FIG. 15 is a flow chart showing contents of step S 16  in FIG. 9. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0043]    An embodiment of the present invention will be described below with reference to FIGS.  1  to  15 .  
         [0044]    The schematic arrangement of an image reading apparatus  60  will be described first with reference to FIG. 1. This image reading apparatus  60  uses, as an original, a negative film or reversal (or positive) film photographed with a camera. The original is held inside a holder  62  and loaded in the image reading apparatus  60 . The holder  62  is supported to freely move in an axial direction indicated by an arrow X by a driving mechanism (not shown). When an electrical motor M 1  (to be described later) is driven, the holder  62  moves in the X-axis direction.  
         [0045]    The image reading apparatus  60  has an illumination unit  50  incorporating a light source unit  20 . FIG. 5 shows the outer appearance of the illumination unit  50 . As shown in FIG. 1, the original in the holder  62  is illuminated from the lower side by the illumination unit  50 . Light transmitted through the original is reflected by a mirror  63  inserted above the original and is incident on the image sensing surface of a linear image sensor  61  through a lens  64 .  
         [0046]    [0046]FIGS. 6 and 7 show the optical path from the light source unit  20  to the image sensing surface of the linear image sensor  61 . To accommodate the illumination optical system in a limited space, the optical path is converted in the illumination unit  50 . More specifically, as shown in FIG. 5, light emitted by the light source unit  20  is reflected by a toric mirror  51  and then by a mirror  52  toward the original. To guide the light reflected by the toric mirror  51  to the mirror  52 , the axis of light emitted by the light source unit  20  is slightly tilted downward. As shown in FIG. 7, the optical path is adjusted by a curved surface R 2  of the toric mirror  51  to illuminate only a small area at the original position in the direction of original movement. As shown in FIG. 6, the optical path is also adjusted by a curved surface R 1  of the toric mirror  51  to illuminate a region corresponding to a full line width at the original position.  
         [0047]    To read a color image, the light source unit  20  of the image reading apparatus  60  can emit a plurality of illumination light components having different wavelengths. More specifically, the R, G, and B color components of the original image can be read using R, G, and B illumination light components, respectively. Especially, in this example, to improve the color reproducibility of an image, the light source unit  20  capable of emitting five illumination light components, i.e., R (red), Y (yellow), G (green), C (cyon), and B (blue) light components is used.  
         [0048]    As shown in FIG. 3, eight light-emitting diode chips  11  to  18  are set on a board  21  constituting the main portion of the light source unit  20 . The light-emitting diode chips  11 ,  12 ,  13 ,  14 ,  15 ,  16 ,  17 , and  18  emit Y, G, R, G, Y, C, B, and C light components, respectively. The light-emitting diode chips  11  and  15  have the same emission characteristics. The light-emitting diode chips  12  and  14  have the same emission characteristics. The light-emitting diode chips  16  and  18  have the same emission characteristics. The emission characteristics of the five light-emitting diode chips  17 ,  16 ,  12 ,  11 , and  13  are shown in FIG. 4 as characteristics P 1 , P 2 , P 3 , P 4 , and P 5 , respectively.  
         [0049]    As shown in FIGS. 2 and 3, the light-emitting diode chips  11 ,  12 ,  13 ,  14 ,  15 ,  16 ,  17 , and  18  are mounted on the bottoms of recesses  21   a ,  21   b ,  21   c ,  21   d ,  21   e ,  21   f ,  21   g , and  21   h  formed in the board  21 , respectively. The inner walls of the recesses  21   a  to  21   h  of the board  21  reflect transverse light emitted by the light-emitting diode chips  11  to  18  in a direction indicated by an arrow Y.  
         [0050]    C illumination light emitted by the light-emitting diode chips  16  and  18  and B illumination light emitted by the light-emitting diode chip  17  are reflected by a surface  23   b  of a spectral filter  23  to travel almost in a direction indicated by an arrow X, as shown in FIG. 2. Y illumination light emitted by the light-emitting diode chips  11  and  15 , G illumination light emitted by the light-emitting diode chips  12  and  14 , and R illumination light emitted by the light-emitting diode chip  13  are reflected by a total reflection mirror  22 , refracted by a surface  23   a  of the spectral filter  23 , transmitted through the spectral filter  23 , and refracted by the surface  23   b  to travel almost in the direction indicated by the arrow X, as shown in FIG. 2. That is, all the R, Y, G, C, and B illumination light components emitted by the light source unit  20  travel in the X direction. Therefore, as shown in FIGS. 1 and 5, the original supported by the holder  62  can be illuminated with the light emitted by the light source unit  20 .  
         [0051]    As shown in FIG. 8, the electrical circuit in the image reading apparatus  60  comprises a main control unit  100 , a sampling unit  110 , an A/D converter  120 , a memory unit  130 , an interface unit  140 , a timing control unit  150 , a digital signal processing unit  160 , a light source control unit  170 , and a subscan control unit  180 . The main control unit  100  controls the entire operation of the image reading apparatus  60 . The main control unit  100  incorporates a microcomputer.  
         [0052]    To read an image, the timing control unit  150  supplies various timing signals (pulse signals) necessary for image reading to the linear image sensor  61 . The linear image sensor  61  reads the image in units of lines in synchronism with the timing signal. Line images read by the linear image sensor  61  are sequentially output in units of pixels as an analog image signal.  
         [0053]    The sampling unit  110  samples the analog image signal output from the linear image sensor  61  in synchronism with the timing signal supplied from the timing control unit  150 . More specifically, the sampling unit  110  extracts the signal level in units of pixels. The analog image signal sampled by the sampling unit  110  is converted into a digital signal by the A/D converter  120  and input to the memory unit  130 . The memory unit  130  has a storage capacity which allows storage of color image data of at least one frame separated into five color components of R, Y, G, C, and B in this example.  
         [0054]    When the five color components of R, Y, G, C, and B of the image are converted into three color components of R, G, and B in units of lines, i.e., color conversion is always performed before the completion of reading one frame image, the storage capacity of the memory unit  130  can be reduced.  
         [0055]    The digital signal processing unit  160  performs predetermined image processing for the image data held by the memory unit  130  in accordance with an instruction from the main control unit  100 . For example, the five color components of R, Y, G, C, and B are converted into three color components of R, G, and B.  
         [0056]    The color image data held by the memory unit  130  is output to the interface unit  140  in response to a request from the host computer connected to the image reading apparatus  60  through the interface unit  140 .  
         [0057]    The light source control unit  170  turns on/off, i.e., ON/OFF-controls the light-emitting diode chips  11  to  18  of the light source unit  20  in accordance with an instruction from the main control unit  100 . Instead of the ON/OFF control, the light source control unit  170  may control the magnitude of an energization current for each light-emitting diode. In either case, the magnitude of the energization current for each light-emitting diode is controlled in accordance with a desired light emission luminance.  
         [0058]    The subscan control unit  180  controls drive of the electrical motor M 1  in accordance with an instruction from the main control unit  100 . The driving shaft of the electrical motor M 1  is coupled to a subscan mechanism (not shown) for moving the holder  62  in the direction indicated by the arrow X.  
         [0059]    [0059]FIG. 9 schematically shows the operation of the main control unit  100 . The contents of the respective steps will be described with reference to FIG. 9. In the following description, processing is executed by the microcomputer incorporated in the main control unit  100  unless otherwise specified.  
         [0060]    In step S 1 , the entire system is initialized. More specifically, the main control unit  100 , and the interface unit  140 , timing control unit  150 , digital signal processing unit  160 , light source control unit  170 , and subscan control unit  180  connected to the main control unit  100  are initialized. With this processing, the electrical motor M 1  is stopped, and all the light-emitting diode chips  11  to  18  of the light source unit  20  are turned off. The main control unit  100  can communicate with a predetermined host computer connected through the interface unit  140 .  
         [0061]    In step S 2 , it is determined whether a predetermined mode designation has been inputted from the host computer. In this example, the image reading apparatus  60  has six reading modes. One of the reading modes is selected in accordance with the designation from the host computer. If YES in step S 2 , the flow advances from step S 2  to step S 3 .  
         [0062]    In step S 3 , the value of the reading mode designated by the host computer is set in a mode register M allocated in the internal memory.  
         [0063]    In step S 4 , it is determined whether predetermined image reading has been ordered by the host computer. If YES in step S 4 , the flow advances from step S 4  to step S 5 .  
         [0064]    In step S 5 , the value held by the mode register M is compared with 1. That is, it is determined whether reading mode “1” has been set. If YES in step S 5 , the flow advances to step S 11 . If NO in step S 5 , the flow advances to step S 6 .  
         [0065]    In step S 6 , the value held by the mode register M is compared with 2. That is, it is determined whether reading mode “2” has been set. If YES in step S 6 , the flow advances to step S 12 . If NO in step S 6 , the flow advances to step S 7 .  
         [0066]    In step S 7 , the value held by the mode register M is compared with 3. That is, it is determined whether reading mode “3” has been set. If YES in step S 7 , the flow advances to step S 13 . If NO in step S 7 , the flow advances to step S 8 .  
         [0067]    In step S 8 , the value held by the mode register M is compared with 4. That is, it is determined whether reading mode “4” has been set. If YES in step S 8 , the flow advances to step S 14 . If NO in step S 8 , the flow advances to step S 9 .  
         [0068]    In step S 9 , the value held by the mode register M is compared with 5. That is, it is determined whether reading mode “5” has been set. If YES in step S 9 , the flow advances to step S 15 . If NO in step S 9 , the flow advances to step S 10 .  
         [0069]    In step S 10 , the value held by the mode register M is compared with 6. That is, it is determined whether reading mode “6” has been set. If YES in step S 10 , the flow advances to step S 16 . If NO in step S 10 , the flow returns to step S 2 .  
         [0070]    In step S 11 , “image reading 1” is executed. Details of this processing are shown in FIG. 10. In “image reading 1”, the color of light emitted by the light source unit  20  is sequentially changed to B, C, G, Y, and R to read the images of color components of B, C, G, Y, and R, respectively. Every time one line of the image is read, the color of light emitted by the light source unit  20  is switched. This processing will be described later in detail.  
         [0071]    In step S 12 , “image reading 2” is executed. Details of this processing are shown in FIG. 11. In “image reading 2”, the color of light emitted by the light source unit  20  is sequentially switched to B, G, and R to read the images of color components B, G, and R, respectively. Every time one line of the image is read, the color of light emitted by the light source unit  20  is switched. This processing will be described later in detail.  
         [0072]    In step S 13 , “image reading 3” is executed. Details of this processing are shown in FIG. 12. In “image reading 3”, the color of light emitted by the light source unit  20  is sequentially switched to B, G, and R to read the images of color components B, G, and R, respectively. Especially, to cause the light source unit  20  to emit B light, not only the light-emitting diode chip  17  for emitting B light but also the light-emitting diode chips  16  and  18  for emitting C light are simultaneously turned on. To cause the light source unit  20  to emit R light, not only the light-emitting diode chip  13  for emitting R light but also the light-emitting diode chips  11  and  15  for emitting Y light are simultaneously turned on. The color of light emitted by the light source unit  20  is switched every time one line of the image is read. Details of this processing will be described later in detail.  
         [0073]    In step S 14 , “image reading 4” is executed. Details of this processing are shown in FIG. 13. In “image reading 4”, the color of light emitted by the light source unit  20  is sequentially switched to B, C, G, Y, and R to read the images of color components B, C, G, Y, and R, respectively. The color of light emitted by the light source unit  20  is switched every time one frame of the image is read. Details of this processing will be described later in detail.  
         [0074]    In step S 15 , “image reading 5” is executed. Details of this processing are shown in FIG. 14. In “image reading 5”, the color of light emitted by the light source unit  20  is sequentially switched to B, G, and R to read the images of color components B, G, and R, respectively. The color of light emitted by the light source unit  20  is switched every time one frame of the image is read. Details of this processing will be described later in detail.  
         [0075]    In step S 16 , “image reading 6” is executed. Details of this processing are shown in FIG. 15. In “image reading 6”, the color of light emitted by the light source unit  20  is sequentially switched to B, G, and R to read the images of color components B, G, and R, respectively. Especially, to cause the light source unit  20  to emit B light, not only the light-emitting diode chip  17  for emitting B light but also the light-emitting diode chips  16  and  18  for emitting C light are simultaneously turned on. To cause the light source unit  20  to emit R light, not only the light-emitting diode chip  13  for emitting R light but also the light-emitting diode chips  11  and  15  for emitting Y light are simultaneously turned on. The color of light emitted by the light source unit  20  is switched every time one frame of the image is read. Details of this processing will be described later in detail.  
         [0076]    [0076]FIG. 9 shows only processing associated with image reading. However, for example, when an image data transfer request is issued from the host computer, image data is output from the memory unit  130  to the interface unit  140  in response to the request. This processing is omitted in FIG. 9. “Image reading 1” executed in reading mode “1”  
         [0077]    will be described in detail with reference to FIG. 10.  
         [0078]    In step S 20 , the contents of counters NC and NL allocated in the internal memory are initialized. The value of the counter NC represents a number assigned to the color of illumination. In this case, the values “0”, “1”, “2”, “3”, and “4” of the counter NC correspond to the B, C, G, Y, and R color components of light emitted by the light source unit  20 , respectively. The value of the counter NL represents the scanning position in the subscan direction (X direction). Every time the images of all color components of one line are read, the value of the counter NL is updated.  
         [0079]    In step S 21 , an instruction is issued to the subscan control unit  180  to start subscan drive. The electrical motor Ml is driven to move the holder  62  for supporting the original in the direction indicated by the arrow X at a predetermined speed. When the holder  62  moves, the relative positional relationship between the image reading position and the original supported by the holder  62  changes.  
         [0080]    In step S 22 , it is determined whether image reading has been completed for one frame. More specifically, the value of the counter NL is compared with a predetermined threshold value to determine whether the scanning position in the subscan direction has moved by a distance corresponding to one frame.  
         [0081]    If NO in step S 22 , the flow advances to step S 23 . If YES in step S 22 , the flow advances to step S 36 .  
         [0082]    In step S 23 , the state of a line synchronizing signal which periodically appears every time one line image is read is monitored to determine whether a predetermined line synchronization timing is detected. If YES in step S 23 , the flow advances from step S 23  to step S 24 .  
         [0083]    In step S 24 , the next processing is selected in accordance with the value of the counter NC. When the value of the counter NC is “0”, “1”, “2”, “3”, or “4”, the flow advances to step S 25 , S 26 , S 27 , S 28 , or S 29 , respectively.  
         [0084]    In step S 25 , the light source control unit  170  is controlled to turn on the light-emitting diode chip  17  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  12 ,  13 ,  14 ,  15 ,  16 , and  18  are turned off. That is, B light is emitted as illumination light.  
         [0085]    In step S 26 , the light source control unit  170  is controlled to turn on the light-emitting diode chips  16  and  18  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  12 ,  13 ,  14 ,  15 , and  17  are turned off. That is, C light is emitted as illumination light.  
         [0086]    In step S 27 , the light source control unit  170  is controlled to turn on the light-emitting diode chip  12  and  14  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  13 ,  15 ,  16 ,  17 , and  18  are turned off. That is, G light is emitted as illumination light.  
         [0087]    In step S 28 , the light source control unit  170  is controlled to turn on the light-emitting diode chips  11  and  15  of the light source unit  20 . All the remaining light-emitting diode chips  12 ,  13 ,  14 ,  16 ,  17 , and  18  are turned off. That is, Y light is emitted as illumination light.  
         [0088]    In step S 29 , the light source control unit  170  is controlled to turn on the light-emitting diode chip  13  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  12 ,  14 ,  15 ,  16 ,  17 , and  18  are turned off. That is, R light is emitted as illumination light.  
         [0089]    In step S 30 , an image is read for one line. More specifically, transmission light from the original illuminated with any one of the B, C, G, Y, and R light components is read by the linear image sensor  61  for one line.  
         [0090]    The signal output from the linear image sensor  61  is input to the memory unit  130  through the sampling unit  110  and A/D converter  120 . The signal input to the memory unit  130  is one of color signal components obtained by separating the image into five colors: B, C, G, Y, and R. The memory unit  130  holds the input color signal for one line in a line buffer allocated in the internal memory. The color signal components of B, C, G, Y, and R are held by different line buffers.  
         [0091]    In step S 31 , the value of the counter NC is updated. Every time step S 31  is executed, the value of the counter NC is incremented by one.  
         [0092]    In step S 32 , the value of the counter NC is compared with a predetermined maximum value “4”. If the value of the counter NC is not more than 4, the flow returns to step S 22  to repeatedly execute the above processing. That is, the image for one line is read again in step S 30 .  
         [0093]    Every time step S 31  is executed, the value of the counter NC changes. For this reason, processing to be executed in steps S 25  to S 29  is switched. That is, the color of light emitted by the light source unit  20  is sequentially switched, so the image of each of the color components of B, C, G, Y, and R for one line is sequentially read.  
         [0094]    Since the holder  62  holding the original moves in the direction indicated by the arrow X at a predetermined speed, the position at which the original is to be read moves every time step S 30  is executed. However, the moving amount during image reading for five lines is very small. Therefore, when step S 30  is repeatedly executed five times, color component data of B, C, G, Y, and R can be obtained substantially at the same position on the original.  
         [0095]    In this example, the holder is continuously driven in the subscan direction. Alternatively, subscan drive may be performed while repeating movement and stop in units of lines. In this case, the image for five lines is read while the holder  62  is at a stand still, so the color component data at the same position can be obtained.  
         [0096]    When the value of the counter NC exceeds  4 , the flow advances to step S 33 . That is, when all color component data of B, C, G, Y, and R are acquired, the flow advances to step S 33 .  
         [0097]    In step S 33 , color calculation for one line image data is executed. A color image signal processed by a device such as a color display or a color printer generally comprises three color signals of R, G, and B, which represent the levels of color components having prescribed wavelengths of R, G, and B, respectively. On the other hand, the signal obtained by processing in step S 30  has five color components of B, C, G, Y, and R. In some cases, the wavelengths of B, G, and R light components emitted by the light source unit  20  do not accurately match the prescribed wavelengths of R, G, and B. Therefore, to generate a color image signal to be processed by a device such as a color display or a color printer, the color signals must be converted. This conversion is executed in step S 33 .  
         [0098]    For the descriptive convenience, B, C, G, Y, and R color components obtained by processing in step S 30  are defined as B 1 , C 1 , G 1 , Y 1 , and R 1 , respectively. In addition, signals of the B 1 , C 1 , G 1 , Y 1  and R 1  color components are defined as DB 1 , DC 1 , DG 1 , DY 1 , and DR 1 , respectively.  
         [0099]    In step S 33 , prescribed color components of R, G, and B are obtained from the signals DB 1 , DC 1 , DG 1 , DY 1 , and DR 1  using following formula (1).  
               [         R           G           B         ]     =       [         K11       K12       K13       K14       K15           K21       K22       K23       K24       K25           K31       K32       K33       K34       K35         ]                [         DR1           DY1           DG1           DC1           DB1         ]             (   1   )                               
 
         [0100]    where K 11  to K 15 , K 21  to K 25 , and K 31  to K 35  are constants.  
         [0101]    In step S 33 , calculation or operation for a large quantity of data must be repeated. Actual calculation is executed at a high speed using the digital signal processing unit  160 .  
         [0102]    In step S 34 , one line image data of R, G, and B generated in step S 33  are stored in a frame memory area allocated in the memory unit  130 . The write address is determined in accordance with the position in the subscan direction, i.e., the contents of the counter NL.  
         [0103]    In step S 35 , the value of the counter NC is cleared to 0. In addition, the value of the counter NL representing the subscan position is updated. The value of the counter NL is incremented every time step S 35  is executed.  
         [0104]    In step S 36 , all the light-emitting diode chips  11  to  18  of the light source unit  20  are turned off. Subscan drive is also stopped.  
         [0105]    When “image reading 1” shown in FIG. 10 is to be executed, the color of image data is reproduced on the basis of the five color components of B 1 , C 1 , G 1 , Y 1 , and R 1  of the read image, so a color image with high color reproducibility can be obtained.  
         [0106]    Color reproducibility in a case wherein the color of image data was reproduced on the basis of four or more color components and that in a case wherein the color of image data was reproduced on the basis of three color components were compared by a computer simulation. As a result, we confirmed that, when the color of image data was reproduced on the basis of four or more color components, the color reproducibility largely improved as compared to the case in which only three colors are used.  
         [0107]    In “image reading 1” shown in FIG. 10, image data is read for each of the five color components.  
         [0108]    However, for example, only four color components of B 1 , C 1 , G 1 , and R 1  or B 1 , G 1 , Y 1 , and R 1  may be read. Even when the image is read for each of the four color components, the color reproducibility sufficiently improves as compared to the prior art. Especially, when a film having four photosensitive layers is used as an original, high color reproducibility can be obtained by reading the image while appropriately selecting the wavelengths of four color components.  
         [0109]    “Image reading 2” executed in reading mode “2” will be described next in detail with reference to FIG. 11. The same numerals as in FIG. 10 denote the same steps in FIG. 11. In FIG. 11, steps S 21 B, S 32 B, S 33 B, S 37 , S 38 , and S 39  are different from FIG. 10. Processing operations different from FIG. 10 will be described below.  
         [0110]    In “image reading 2” shown in FIG. 11, only three colors of R, G, and B are used as illumination colors. Hence, the three color components of R, G, and B of the original image are sequentially read.  
         [0111]    When the value of the counter NC is 0, step S 37  is executed. In step S 37 , the light source control unit  170  is controlled to turn on the light-emitting diode chip  17  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  12 ,  13 ,  14 ,  15 ,  16 , and  18  are turned off. That is, the B light is emitted as illumination light.  
         [0112]    When the value of the counter NC is 1, step S 38  is executed. In step S 38 , the light source control unit  170  is controlled to turn on the light-emitting diode chips  12  and  14  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  13 ,  15 ,  16 ,  17 , and  18  are turned off. That is, the G light is emitted as illumination light.  
         [0113]    When the value of the counter NC is 2, step S 39  is executed. In step S 39 , the light source control unit  170  is controlled to turn on the light-emitting diode chip  13  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  12 ,  14 ,  15 ,  16 ,  17 , and  18  are turned off. That is, the R light is emitted as illumination light.  
         [0114]    In step S 32 B, the value of the counter NC is compared with a predetermined maximum value “2”. If the value of the counter NC is not more than 2, the flow returns to step S 22  to repeat step S 30 . That is, image reading for one line is repeated.  
         [0115]    When step S 31  is executed, the value of the counter NC changes, so processing to be executed in steps S 37  to S 39  is switched. That is, the color of light emitted by the light source unit  20  is sequentially switched, so the image of each of the color components of B, G, and R for one line is sequentially read.  
         [0116]    Since the holder  62  holding the original moves in the direction indicated by the arrow X at a predetermined speed, the position at which the original is to be read moves every time step S 30  is executed. However, the moving amount during image reading for three lines is very small. Therefore, when step S 30  is repeated three times, color component data of B, G, and R can be obtained substantially at the same position on the original.  
         [0117]    The subscan speed determined in step S 21 B is larger than that in step S 21  in FIG. 10. In “image reading 1” in FIG. 10, the image is read five times per line of the output image. In “image reading 2” in FIG. 11, the image is read three times per line of the output image. Hence, when processing shown in FIG. 11 is executed, the reading time per line of the image is shorter than that in processing shown in FIG. 10.  
         [0118]    In step S 21 B, the subscan speed is determined on the basis of the reading time per line of the image. Since the reading time per line of the image is shorter, the subscan speed in step S 21 B is higher than that in step S 21 .  
         [0119]    When the value of the counter NC exceeds 2, the flow advances to step S 33 B. That is, when all color component data of B, G, and R are acquired for one line, the flow advances to step S 33 B.  
         [0120]    In step S 33 B, color calculation for one line image data is executed. Step S 33 B is different from step S 33  only in the contents of calculation.  
         [0121]    The signal obtained by processing in step S 30  has three color components of B, G, and R. In some cases, the wavelengths of B, G, and R light components emitted by the light source unit  20  do not accurately match the prescribed wavelengths of R, G, and B. Therefore, to generate a color image signal to be processed by a device such as a color display or a color printer, the color signals are converted in step S 33 B. For the descriptive convenience, B, G, and R color components obtained by processing in step S 30  are defined as B 1 , G 1 , and R 1 , respectively. In addition, signals of the B 1 , G 1 , and R 1  color components are defined as DB 1 , DG 1 , and DR 1 , respectively.  
         [0122]    In step S 33 B, prescribed color components of R, G, and B are obtained from the signals DB 1 , DG 1 , and DR 1  using following formula (2).  
               [         R           G           B         ]     =       [         K11B       K12B       K13B           K21B       K22B       K23B           K31B       K32B       K33B         ]                [         DR1           DG1           DB1         ]             (   2   )                               
 
         [0123]    where K11B to K13B, K21B to K23B, and K31B to K33B are constants.  
         [0124]    In step S 33 B, calculation for a large quantity of data must be repeated. Actual calculation is executed at a high speed using the digital signal processing unit  160 .  
         [0125]    The operation realized by “image reading 2” shown in FIG. 11 is basically the same as that of the conventional operation. That is, when reading mode “2” is designated, the same operation as that of the conventional apparatus is executed. For example, when an image on an original having relatively low image quality is read, particularly high color reproducibility is unnecessary. For this reason, “image reading 2” shown in FIG. 11 may be performed. Since the subscan speed of processing shown in FIG. 11 is higher than that of processing in FIG. 10, the entire image of the original can be read in a short time. “Image reading 3” executed in reading mode “3”  
         [0126]    will be described next in detail with reference to FIG. 12. The same numerals as in FIG. 10 denote the same steps in FIG. 12.  
         [0127]    In FIG. 12, steps S 21 C, S 32 B, S 33 C, S 41 , S 38 , and S 42  are different from FIG. 10. Processing operations different from FIG. 10 will be described below.  
         [0128]    In “image reading 3” shown in FIG. 12, only three colors of R, G, and B are used as illumination colors. Hence, the three color components of R, G, and B of the original image are sequentially read. However, the illumination colors of R and B in FIG. 12 are slightly different from those in FIG. 10.  
         [0129]    When the value of the counter NC is 0, step S 41  is executed. In step S 41 , the light source control unit  170  is controlled to turn on the light-emitting diode chips  16 ,  17 , and  18  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  12 ,  13 ,  14 , and  15  are turned off.  
         [0130]    As shown in FIG. 4, the wavelength of C is relatively close to the wavelength of B. When the two types of light-emitting diode chips  16 ,  17 , and  18  are simultaneously turned on, illumination light having a wavelength which can substantially be classified into B can be obtained. When the two types of light-emitting diode chips  16 ,  17 , and  18  are turned on, the emission intensity becomes higher than that in a case wherein only one type of light-emitting diode chip  17  is turned on.  
         [0131]    When the value of the counter NC is 1, step S 38  is executed. In step S 38 , the light source control unit  170  is controlled to turn on the light-emitting diode chips  12  and  14  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  13 ,  15 ,  16 ,  17 , and  18  are turned off. That is, G light is emitted as illumination light.  
         [0132]    When the value of the counter NC is 2, step S 42  is executed. In step S 42 , the light source control unit  170  is controlled to turn on the light-emitting diode chips  11 ,  13 , and  15  of the light source unit  20 . All the remaining light-emitting diode chips  12 ,  14 ,  16 ,  17 , and  18  are turned off.  
         [0133]    As shown in FIG. 4, the wavelength of Y is relatively close to the wavelength of R. When the two types of light-emitting diode chips  11 ,  13 , and  15  are simultaneously turned on, illumination light having a wavelength which can substantially be classified into R can be obtained. When the two types of light-emitting diode chips  11 ,  13 , and  15  are turned on, the emission intensity becomes higher than that in a case wherein only one type of light-emitting diode chip  13  is turned on.  
         [0134]    In step S 32 B, the value of the counter NC is compared with a predetermined maximum value “2”. If the value of the counter NC is not more than 2, the flow returns to step S 22  to repeat step S 30 . That is, image reading for one line is repeated.  
         [0135]    When step S 31  is executed, the value of the counter NC changes, so processing to be executed in steps S 41 , S 38 , and S 42  is switched. That is, the color of light emitted by the light source unit  20  is sequentially switched, so the image of each of the color components of B, G, and R for one line is sequentially read.  
         [0136]    Since the holder  62  holding the original moves in the direction indicated by the arrow X at a predetermined speed, the position at which the original is to be read moves every time step S 30  is executed. However, the moving amount during image reading for three lines is very small. Therefore, when step S 30  is repeated three times, color component data of B, G, and R can be obtained essentially at the same position on the original.  
         [0137]    The subscan speed determined in step S 21 C is much larger than that in step S 21  or S 21 B. In “image reading 2” in FIG. 11 and “image reading 3” in FIG. 12, the image is read three times per line of the output image. However, in “image reading 3” in FIG. 12, a plurality of types of light-emitting diode chips are simultaneously turned on to obtain the B and G illumination light components. For this reason, the illumination intensity of processing in FIG. 12 is higher than that of processing in FIG. 11. When the illumination intensity is high, the original exposure time (charging time of the linear image sensor  61 ) can be shortened. The reading time per line of the image is also shortened.  
         [0138]    In step S 21 C, the subscan speed is determined on the basis of the reading time per line of the image. Since the reading time per line of the image is shorter, the subscan speed in step S 21 C is higher than that in step S 21 B.  
         [0139]    When YES in step S 32 B, i.e., the value of the counter NC exceeds  2 , the flow advances to step S 33 C. That is, when all color component data of B, G, and R are acquired for one line, the flow advances to step S 33 C.  
         [0140]    In step S 33 C, color calculation for one line image data is executed. Step S 33 C, S 33 , and S 33 B are different only in the contents of calculation.  
         [0141]    The signal obtained by processing in step S 30  has three color components of B, G, and R. In some cases, the wavelengths of B, G, and R light components emitted by the light source unit  20  do not accurately match the prescribed wavelengths of R, G, and B. Therefore, to generate a color image signal to be processed by a device such as a color display or a color printer, the color signals are converted in step S 33 C. For the descriptive convenience, B, G, and R color components obtained by processing in step S 30  are defined as B 2 , G 1 , and R 2 , respectively. In addition, signals of the B 2 , G 1 , and R 2  color components are defined as DB 2 , DG 1 , and DR 2 , respectively.  
         [0142]    In step S 33 C, prescribed color components of R, G, and B are obtained from the signals DB 2 , DG 1 , and DR 2  by following formula (3).  
               [         R           G           B         ]     =       [         K11C       K12C       K13C           K21C       K22C       K23C           K31C       K32C       K33C         ]                [         DR2           DG2           DB2         ]             (   3   )                               
 
         [0143]    where K11C to K13C, K21C to K23C, and K31C to K33C are constants.  
         [0144]    In step S 33 C, calculation for a large quantity of data must be repeated. Actual calculation is executed at a high speed using the digital signal processing unit  160 .  
         [0145]    When “image reading 3” shown in FIG. 12 is executed, the entire image of the original can be read in a time shorter than in “image reading 2” shown in FIG. 11. However, the color reproducibility of the image is slightly lower in “image reading 3” than in “image reading 2”. However, when an image or an original having relatively low image quality is read, particularly high color reproducibility is unnecessary. For this reason, “image reading 3” shown in FIG. 12 may be performed in accordance with user&#39;s intention.  
         [0146]    When “image reading 1”, “image reading 2”, or “image reading 3” is executed, the color component to be read is sequentially switched every time one line of the image is scanned. On the other hand, when “image reading 4” shown in FIG. 13, “image reading 5” shown in FIG. 14, or “image reading 6” shown in FIG. 15 is executed, the color component to be read is sequentially switched every time one frame of the image is scanned.  
         [0147]    “Image reading 4” executed in reading mode “4” will be described in detail with reference to FIG. 13.  
         [0148]    In step S 50 , the contents of the counters NC and NL allocated in the internal memory are initialized. The value of the counter NC represents the number assigned to the color of illumination. Actually, the value “0”, “1”, “2”, “3”, and “4” of the counter NC correspond to the B, C, G, Y, and R color components of light emitted by the light source unit  20 , respectively. The value of the counter NL represents the scanning position in the subscan direction (X direction). Actually, every time one line image is read, the value of the counter NL is updated.  
         [0149]    In step S 51 , an instruction is issued to the subscan control unit  180  to start subscan drive. The electrical motor M 1  is driven to move the holder  62  for supporting the original in the direction indicated by the arrow X at a predetermined speed. The holder  62  may be driven stepwise using a stepping motor as the electrical motor M 1 .  
         [0150]    When the holder  62  moves, the relative positional relationship between the image reading position and the original supported by the holder  62  changes.  
         [0151]    In step S 52 , the next processing is selected in accordance with the value of the counter NC. When the value of the counter NC is “0”, “1”, “2”, “3”, or “4”, the flow advances to step S 53 , S 54 , S 55 , S 56 , or S 57 , respectively.  
         [0152]    In step S 53 , the light source control unit  170  is controlled to turn on the light-emitting diode chip  17  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  12 ,  13 ,  14 ,  15 ,  16 , and  18  are turned off. That is, B light is emitted as illumination light.  
         [0153]    In step S 54 , the light source control unit  170  is controlled to turn on the light-emitting diode chips  16  and  18  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  12 ,  13 ,  14 ,  15 , and  17  are turned off. That is, C light is emitted as illumination light.  
         [0154]    In step S 55 , the light source control unit  170  is controlled to turn on the light-emitting diode chip  12  and  14  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  13 ,  15 ,  16 ,  17 , and  18  are turned off. That is, G light is emitted as illumination light.  
         [0155]    In step S 56 , the light source control unit  170  is controlled to turn on the light-emitting diode chips  11  and  15  of the light source unit  20 . All the remaining light-emitting diode chips  12 ,  13 ,  14 ,  16 ,  17 , and  18  are turned off. That is, Y light is emitted as illumination light.  
         [0156]    In step S 57 , the light source control unit  170  is controlled to turn on the light-emitting diode chip  13  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  12 ,  14 ,  15 ,  16 ,  17 , and  18  are turned off. That is, R light is emitted as illumination light.  
         [0157]    In step S 58 , it is determined whether image reading has been completed for one frame. More specifically, the value of the counter NL is compared with a predetermined threshold value to determine whether the scanning position in the subscan direction has moved by one frame. If NO in step S 58 , the flow advances to step S 59 . If YES in step S 58 , the flow advances to step S 62 .  
         [0158]    In step S 59 , the state of a line synchronizing signal which periodically appears every time one line image is read is monitored to determine whether a predetermined line synchronization timing is detected. If YES in step S 59 , the flow advances from step S 59  to step S 60 .  
         [0159]    In step S 60 , an image is read for one line. More specifically, transmission light from the original illuminated with any one of the B, C, G, Y, and R light components is read by the linear image sensor  61  for one line.  
         [0160]    The signal output from the linear image sensor  61  is input to the memory unit  130  through the sampling unit  110  and A/D converter  120 . The signal input to the memory unit  130  is one of color signal components obtained by separating the image into five colors: B, C, G, Y, and R.  
         [0161]    The memory unit  130  holds the input color signal for one line in a frame memory area allocated in the internal memory. The write address is determined in accordance with the counter NL. The color signal components of B, C, G, Y, and R are held by different frame memories.  
         [0162]    In step S 61 , the value of the counter NC is updated. Every time step S 61  is executed, the value of the counter NC is incremented by one.  
         [0163]    Processing in step S 60  is repeated until the completion of image reading for one frame is detected in step S 58 . Therefore, an image signal of one frame associated with any one of colors B, C, G, Y, and R is stored in one frame memory area of the memory unit  130 .  
         [0164]    When image reading for one frame associated with one color is completed the flow advances from step S 58  to step S 62 .  
         [0165]    In step S 62 , the value of the counter NL is initialized to 0. In addition, the value of the counter NC is updated. The value of the counter NC is incremented by one every time step S 62  is executed.  
         [0166]    In step S 63 , the value of the counter NC is compared with a predetermined maximum value “4”. If the value of the counter NC is not more than 4, the flow advances to step S 64 . When the value of the counter NC exceeds  4 , the flow advances to step S 65 .  
         [0167]    In step S 64 , the electrical motor Ml is controlled through the subscan control unit  180  to return the subscan position to the reading start position. More specifically, the driving direction of the electrical motor Ml is reversed to move the holder  62  to the position at which step S 51  has been executed. After this, the driving direction of the electrical motor M 1  is reversed again to return the moving direction of the holder  62  to the forward direction of subscan. That is, the holder  62  is reciprocally driven in the direction indicated by the arrow X every time one frame image associated with one color is read. After step S 64  is executed, the flow returns to step S 52 . Image reading for one frame and one color is executed again by processing in steps S 58  to S 61 .  
         [0168]    When step S 62  is executed, the value of the counter NC changes, so processing to be executed in steps S 53  to S 57  is switched. That is, the color of light emitted by the light source unit  20  is sequentially switched, so the image of each of the color components of B, C, G, Y, and R for one frame is sequentially read.  
         [0169]    When the value of the counter NC exceeds  4 , the flow advances from step S 63  to step S 65 . That is, when all color component data of B, C, G, Y, and R for one frame image have been acquired, the flow advances to step S 65 .  
         [0170]    In step S 65 , all the light-emitting diode chips  11  to  18  of the light source unit  20  are turned off. Subscan drive is also stopped.  
         [0171]    In step S 66 , color calculation is executed for all image data of one frame. The contents of processing are the same as in step S 33  except that the data to be processed is data of one frame.  
         [0172]    More specifically, prescribed color components of R, G, and B are obtained from the signals DB 1 , DC 1 , DG 1 , DY 1 , and DR 1  using formula (1) above. The R, G, and B image data for one frame, which are generated in step S 66 , are stored in frame memory areas allocated in the memory unit  130 .  
         [0173]    “Image reading 5” executed in reading mode “5” will be described next in detail with reference to FIG. 14. The same numerals as in FIG. 13 denote the same steps in FIG. 14.  
         [0174]    In FIG. 14, steps S 63 B, S 66 B, S 71 , S 72 , and S 73  are different from FIG. 13. Processing operations different from FIG. 13 will be described below.  
         [0175]    In “image reading 5” shown in FIG. 14, only three colors of R, G, and B are used as illumination colors. Hence, the three color components of R, G, and B of the original image are sequentially read.  
         [0176]    When the value of the counter NC is 0, step S 71  is executed. In step S 71 , the light source control unit  170  is controlled to turn on the light-emitting diode chip  17  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  12 ,  13 ,  14 ,  15 ,  16 , and  18  are turned off. That is, B light is emitted as illumination light.  
         [0177]    When the value of the counter NC is 1, step S 72  is executed. In step S 72 , the light source control unit  170  is controlled to turn on the light-emitting diode chips  12  and  14  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  13 ,  15 ,  16 ,  17 , and  18  are turned off. That is, G light is emitted as illumination light.  
         [0178]    When the value of the counter NC is 2, step S 73  is executed. In step S 73 , the light source control unit  170  is controlled to turn on the light-emitting diode chip  13  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  12 ,  14 ,  15 ,  16 ,  17 , and  18  are turned off. That is, R light is emitted as illumination light.  
         [0179]    In step S 63 B, the value of the counter NC is compared with a predetermined maximum value “2”. If the value of the counter NC is not more than 2, the flow returns to step S 52  via step S 64  to repeat steps S 58  to S 61 . That is, image reading for one frame and one color is repeated.  
         [0180]    When the value of the counter NC exceeds 2, the flow advances to step S 66 B via step S 65 . That is, when all color component data of B, G, and R for one frame image are acquired, the flow advances to step S 66 B.  
         [0181]    In step S 66 B, color calculation is executed for all image data of one frame. Steps S 66 B and S 66  are different only in the contents of processing. That is, the contents of processing are the same as in step S 33 B except that the data to be processed is data of one frame. More specifically, prescribed color components of R, G, and B are obtained from the signals DB 1 , DG 1 , and DR 1  using formula (2) above. The R, G, and B image data for one frame, which are generated in step S 66 B, are stored in frame memory areas assigned on the memory unit  130 .  
         [0182]    The operation realized by “image reading 5” shown in FIG. 14 is basically the same as that of the conventional operation. That is, when reading mode “5” is designated, the same operation as that of the conventional apparatus is executed. For example, when an image on an original having relatively low image quality is to be read, particularly high color reproducibility is unnecessary. For this reason, “image reading 5” shown in FIG. 14 may be performed. Since the number of times of frame scanning for image reading is smaller in processing shown in FIG. 14 than that in processing in FIG. 13, the entire image of the original can be read in a short time.  
         [0183]    “Image reading 6” executed in reading mode “6” will be described next in detail with reference to FIG. 15. The same numerals as in FIG. 13 denote the same steps in FIG. 15.  
         [0184]    In FIG. 15, steps S 51 C, S 63 B, S 66 C, S 74 , S 75 , and S 76  are different from FIG. 13. Processing operations different from FIG. 13 will be described below.  
         [0185]    In “image reading 6” shown in FIG. 15, only three colors of R, G, and B are used as illumination Colors. Hence, the three color components of R, G, and B of the original image are sequentially read. However, the illumination colors of R and B in FIG. 15 are slightly different from those in FIG. 13.  
         [0186]    When the value of the counter NC is 0, step S 74  is executed. In step S 74 , the light source control unit  170  is controlled to turn on the light-emitting diode chips  16 ,  17 , and  18  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  12 ,  13 ,  14 , and  15  are turned off.  
         [0187]    As shown in FIG. 4, the wavelength of C is reatively close to the wavelength of B. When the two types of light-emitting diode chips  16 ,  17 , and  18  are simultaneously turned on, illumination light having a wavelength which can substantially be classified into B can be obtained. When the two types of light-emitting diode chips  16 ,  17 , and  18  are turned on, the emission intensity becomes higher than that in a case wherein only one type of light-emitting diode chip  17  is turned on.  
         [0188]    When the value of the counter NC is 1, step S 75  is executed. In step S 75 , the light source control unit  170  is controlled to turn on the light-emitting diode chips  12  and  14  of the light source unit  20 . All the remaining light-emitting diode chips  11 ,  13 ,  15 ,  16 ,  17 , and  18  are turned off. That is, G light is emitted as illumination light.  
         [0189]    When the value of the counter NC is 2, step S 76  is executed. In step S 76 , the light source control unit  170  is controlled to turn on the light-emitting diode chips  11 ,  13 , and  15  of the light source unit  20 . All the remaining light-emitting diode chips  12 ,  14 ,  16 ,  17 , and  18  are turned off.  
         [0190]    As shown in FIG. 4, the wavelength of Y is relatively close to the wavelength of R. When the two types of light-emitting diode chips  11 ,  13 , and  15  are simultaneously turned on, illumination light having a wavelength which can substantially be classified into R can be obtained. When the two types of light-emitting diode chips  11 ,  13 , and  15  are turned on, the emission intensity becomes higher than that in a case wherein only one type of light-emitting diode chip  13  is turned on.  
         [0191]    In step S 63 B, the value of the counter NC is compared with a predetermined maximum value “2”. If the value of the counter NC is not more than 2, the flow returns to step S 52  via step S 64  to repeat steps S 58  to S 61 . That is, image reading for one frame and one color is repeated.  
         [0192]    The subscan speed determined in step S 51 C is much higher than that in step S 51 .  
         [0193]    In “image reading 6” in FIG. 15, a plurality of types of light-emitting diode chips are simultaneously turned on to obtain the B and G illumination light components. For this reason, the illumination intensity is higher in processing shown in FIG. 15 than that in processing in FIG. 13 or  14 .  
         [0194]    When the illumination intensity is high, the original exposure time (charging time) of the linear image sensor  61  can be shortened. The reading time per frame of the image is also shortened.  
         [0195]    In step S 51 C, the subscan speed is determined on the basis of the charging time per line of the image. Since the reading time per frame of the image is shorter, the subscan speed in step S 51 C is higher than that in step S 51 .  
         [0196]    When the value of the counter NC exceeds 2, the flow advances to step S 66 C via step S 65 . That is, when all color component data of B, G, and R for one frame image have been acquired, the flow advances to step S 66 C.  
         [0197]    In step S 66 C, color calculation is executed for all image data of one frame. Step S 66 C is different from step S 66  or S 66   b  only in the contents of processing. That is, the contents of processing are the same as in step S 33 C except that the data to be processed is data of one frame. More specifically, prescribed color components of R, G, and B are obtained from the signals DB 2 , DG 1 , and DR 2  using formula (3) above. The R, G, and B image data for one frame, which are generated in step S 66 C, are stored in frame memory areas assigned on the memory unit  130 .  
         [0198]    When “image reading 6” shown in FIG. 15 is executed, the entire image of the original can be read in a time shorter than in “image reading 5” shown in FIG. 14. However, the color reproducibility of the image is slightly lower in “image reading 6” than in “image reading 5”. However, when an image reading on an original having relatively low image quality is to be read, particularly high color reproducibility is unnecessary. For this reason, “image reading 6” shown in FIG. 15 may be performed in accordance with the user&#39;s intention.  
         [0199]    In this embodiment, the image reading apparatus  60  for reading a film-shaped original has been described. However, the present invention can also be practiced for a general image scanner.  
         [0200]    In the above embodiment, the light source unit  20  uses five types of light-emitting devices having different peak emission wavelengths in the visible light range. However, four types of light-emitting devices may be used. Alternatively, the number of types of light-emitting devices may be increased to six or more.  
         [0201]    In the above embodiment, the output color image data has R, G, and B color components. However, only by changing the contents of formulas (1), (2), and (3), data of the XYZ color system or Lab calorimetric system can also be output.  
         [0202]    In the above embodiment, color conversion using formulas (1), (2), and (3) is executed inside the image reading apparatus  60 . However, this color conversion may be omitted, and instead, color conversion may be executed on the host computer side.