Abstract:
An object of this invention is to read a high-quality image by detecting and correcting dirt, a scratch, or a watermark present on an original in an image reading apparatus for reading an original. To achieve this object, an original illumination unit in the image reading apparatus for reading an original includes a first light source for emitting light in at least the visible region, a second light source for emitting light in only the invisible region, and a light guide plate which has these light sources at an end face and distributes incident light from the end face to the entire flat surface.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an image reading apparatus for reading image information of an original and an illumination apparatus used in the image reading apparatus.  
         BACKGROUND OF THE INVENTION  
         [0002]    There is conventionally known an image reading apparatus for illuminating a transparent original and reading its image, as disclosed in U.S. Pat. No. 5,038,227. The conventional image reading apparatus will be described with reference to FIGS. 7A and 7B.  
           [0003]    [0003]FIG. 7A is a sectional view showing an image reading apparatus, and FIG. 7B is a perspective view. A bar-like fluorescent tube  700  is attached to the end of a light guide plate  701  which is arranged in parallel to a platen glass  702  for supporting an original. The light guide plate  701  is a resin light diffusion panel for diffusing light emitted by the fluorescent tube  700  and emitting the light from the surface.  
           [0004]    The platen glass  702  is an original table for supporting a transparent original such as a photographic film. A transparent original on the platen glass  702  is sandwiched and fixed between the light guide plate  701  and the platen glass  702 . A CCD  703  is a linear imaging element for converting image information into an electric image signal. An imaging optical system  704  optically guides the image information of the transparent original to the CCD  703 .  
           [0005]    A carriage  705  supports the CCD  703  and imaging optical system  704 , and is movable in the subscanning direction along guides  706  and  707 . When the entire surface of a transparent original is illuminated by the light guide plate  701 , image information of the transparent original is read by the CCD  703  via the imaging optical system  704 . The carriage  705  is moved in the subscanning direction to sequentially read the image of the entire transparent original.  
           [0006]    If, however, dirt such as dust exists on a transparent original or a film surface is scratched, the conventional image reading apparatus reads even the dirt or scratch, so the image degrades owing to the dirt or scratch.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention has been made in consideration of the above situation, and has as its object to provide an image reading apparatus and illumination apparatus capable of preventing degradation of an image caused by dirt, a scratch, or watermark information on an original surface.  
           [0008]    To overcome the conventional drawbacks and achieve the above object, an image reading apparatus according to the first aspect of the present invention has the following arrangement.  
           [0009]    That is, an image reading apparatus for forming light from an original into an image on a solid-state image sensing element by using an imaging optical system, and reading image information of the original comprises a first light source for emitting light of a visible region, a second light source for emitting light of an invisible region, a light guide plate which has the first and second light sources at an end face, guides incident light from the end face along a surface, and emits the incident light from the surface, image information reading means for reading the image information recorded on the original on the basis of an image signal obtained by guiding, to the solid-state image sensing element, light from the original illuminated with light from the first light source that is guided by the light guide plate, information reading means for reading second information present on an optical path extending from the light guide plate to the solid-state image sensing element on the basis of an image signal obtained by guiding, to the solid-state image sensing element, light from the original illuminated with light from the second light source that is guided by the light guide plate, and correction means for removing the second information read by the information reading means from the image information read by the image information reading means.  
           [0010]    An image reading apparatus according to the second aspect of the present invention has the following arrangement.  
           [0011]    That is, an image reading apparatus comprises a first light source for mainly emitting light of a visible region, a second light source for mainly emitting light of an invisible region, a light guide plate for guiding light emitted by the first and second light sources along a surface and illuminating an original, and reading means for converting, into an image signal, transmitted light of the transparent original illuminated with light from the first or second light source that is guided by the light guide plate.  
           [0012]    An illumination apparatus according to the present invention has the following arrangement.  
           [0013]    That is, an illumination apparatus used in an image reading apparatus for forming light from an original into an image on a solid-state image sensing element by using an imaging optical system, and reading image information of the original comprises a first light source for emitting light of a visible region, a second light source for emitting light of an invisible region, and a light guide plate which has the first and second light sources at an end face, guides incident light from the end face along a surface, and uniformly emits the light.  
           [0014]    Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part hereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a block diagram showing the arrangement of an image reading apparatus according to the first embodiment;  
         [0016]    [0016]FIG. 2 is a schematic perspective view showing the image reading apparatus according to the first embodiment;  
         [0017]    [0017]FIG. 3 is a schematic perspective view showing a transmission illumination unit according to the first embodiment;  
         [0018]    [0018]FIG. 4 is a schematic sectional view showing the transmission illumination unit according to the first embodiment;  
         [0019]    [0019]FIG. 5 is a sectional view showing the image reading apparatus according to the first embodiment;  
         [0020]    [0020]FIG. 6 is a schematic perspective view showing a transmission illumination unit according to the second embodiment; and  
         [0021]    [0021]FIGS. 7A and 7B are a sectional view and perspective view, respectively, showing a conventional image reading apparatus. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    (First Embodiment)  
         [0023]    An image reading apparatus according to the first embodiment of the present invention will be described with reference to the accompanying drawings.  
         [0024]    [0024]FIG. 1 is a block diagram showing the internal arrangement of the image reading apparatus according to the first embodiment. Respective functional blocks will be explained with reference to FIG. 1. An image reading apparatus  1  is connected to a host computer  21  via a signal cable. The image reading apparatus  1  operates to read an image in accordance with an instruction from the host computer  21 , and transfers the image signal to the host computer  21 .  
         [0025]    Reference numeral  105  denotes an imaging lens for forming light from an original irradiated by a light source  3  into an image on a CCD  106  serving as a solid-state image sensing element; and  24 , a light controller for turning on the light source  3 . Note that the image sensing element may be a CMOS or the like other than the CCD. On an electric board  16 , reference numeral  25  denotes a motor driver for driving a pulse motor  6  and outputting an excitation switching signal for the pulse motor  6  upon reception of a signal from a system controller  26  serving as the system control means of the image reading apparatus (image scanner)  1 ; and  27 R,  27 G, and  27 B, analog gain adjusters for variously amplifying analog image signals output from the CCD line sensor  106 .  
         [0026]    Reference numeral  28  denotes an A/D converter for converting analog image signals output from the analog gain adjusters  27 R,  27 G, and  27 B into digital image signals;  29 , an image processor for performing image processing such as offset correction, shading correction, digital gain adjustment, color balance adjustment, masking, resolution conversion in the main scanning and subscanning directions for a digital image signal; and  30 , a line buffer which temporarily stores image data and is realized by a general-purpose random access memory.  
         [0027]    Reference numeral  31  denotes an interface for communicating with the host  21 . In this embodiment, the interface  31  is realized by a SCSI controller but may adopt another interface such as a centronics or USB. Reference numeral  32  denotes an offset RAM used as a working area in image processing. The offset RAM  32  is used to correct offsets between R, G, and B lines because the line sensor  106  is constituted by parallel-arranging R, G, and B line sensors with predetermined offsets. The offset RAM  32  also temporarily stores various data for shading correction and the like. In this embodiment, the offset RAM  32  is realized by a general-purpose random access memory.  
         [0028]    Reference numeral  33  denotes a gamma RAM for storing a gamma curve for gamma correction. The system controller  26  stores the sequence of the overall scanner as a program, and executes various control processes in accordance with instructions from the host  21 . Reference numeral  34  denotes a CPU bus which connects the system controller  26  to the image processor  29 , line buffer  30 , interface  31 , offset RAM  32 , and gamma RAM  33 , and is made up of address and data buses.  
         [0029]    [0029]FIG. 2 is a schematic perspective view showing the image reading apparatus according to the first embodiment. As shown in FIG. 2, a transmission illumination unit  2  for illuminating a transparent original in reading the transparent original such as a developed photographic film is pivotally attached to the image reading apparatus  1  through a hinge  18 . The transmission illumination unit  2  is attached by fixing the surface light source  3  (to be described later) to a lower unit cover  5  with a screw or the like. The surface light source  3  is protected with a transparent member for protecting a light source.  
         [0030]    The main body of the image reading apparatus  1  is equipped with a platen glass  13  for supporting an original to be read. To read a photographic film, a light-shielding sheet  4  is placed on the platen glass  13 . A shading window  4   a  of the light-shielding sheet  4  is to measure shading, and a transmission original support portion  4   b  is a location where a transparent original is placed.  
         [0031]    [0031]FIG. 3 is a schematic perspective view showing the transmission illumination unit  2 , and FIG. 4 is a sectional view showing the surface light source  3 . The light source  3  is constituted by a light guide plate  19 , transparent original reading lamps  6  such as fluorescent tubes or xenon lamps, and dirt/scratch detection lamps  7  formed from LEDs having an emission intensity in only the infrared region. The transparent original illumination lamps  6  emit light of only the visible region, but may emit light of the invisible region such as the infrared region as far as the lamps  6  mainly emit light of the visible region. The dirt/scratch detection lamps  7  suffice to mainly emit light of the infrared region instead of emitting only light of the infrared region. Moreover, a light source other than a fluorescent tube, xenon lamp, and LED may be used. The transparent original reading lamps  6  and dirt/scratch detection lamps  7  are parallel-arranged in the vertical direction along two sides perpendicular to the moving direction of a carriage  9  in the longitudinal direction of the light guide plate  19 . The central axis (e) of each lamp  6  is arranged nearer the center (d) of thickness of the light guide plate  19  than the central axis (f) of a corresponding lamp  7 . That is, |d−e|&lt;|d−f| holds, which increases the space efficiency. Note that the lamps  6  and  7  suffice to be arranged along at least one side, and may be arranged along sides parallel to the moving direction of the carriage  9 . Each lamp  6  and each lamp  7  need not be vertically arranged.  
         [0032]    The light guide plate  19  is a resin light guide diffusion panel comprised of a light guide portion  11  for guiding illumination light L in a two-dimensional longitudinal direction by internal reflection, a reflection sheet  10  for reflecting in the original direction the light guided by the light guide portion  11 , and a diffusion sheet  12  for making the light reflected by the reflection sheet  10  uniform.  
         [0033]    Light L emitted by the transparent original reading lamps  6  and dirt/scratch detection lamps  7  propagates through the light guide portion  11  in the two-dimensional longitudinal direction while being reflected between the reflection sheet  10  and the diffusion sheet  12 . Part of the light incident on the diffusion sheet  12  diffuses, and the entire surface of the light guide plate  19  emits light.  
         [0034]    [0034]FIG. 5 is a sectional view showing the image reading apparatus according to the first embodiment. The carriage  9  of the image reading apparatus  1  supports a reflection original illumination lamp  20 , the CCD line sensor  106 , the lens  105 , and a reflecting mirror  16 . The CCD line sensor  106  converts an image into an electric image signal and is constituted by a plurality of aligned image sensing elements. The carriage  9  is fit on a carriage guide shaft  8  and is movable in the subscanning direction.  
         [0035]    Reading operation of a transparent original will be described.  
         [0036]    The reflection original illumination lamp  20  and dirt/scratch detection lamp  7  are turned off, the transparent original lamp  6  is turned on, and the whole surface light source  3  emits light. The carriage  9  is moved in the subscanning direction to project image information on the transparent original onto the CCD  106  through the reflecting mirror  16  and lens  105 .  
         [0037]    Subsequently, the reflection original illumination lamp  20  and transparent original illumination lamp  6  are turned off, the dirt/scratch detection lamp  7  is turned on, and the whole surface light source  3  emits light. The carriage  9  is moved in the subscanning direction to project dirt, a scratch, or the like on the transparent original onto the CCD  106  through the reflecting mirror  16  and lens  105 . Since light from the dirt/scratch detection lamp  7  includes only an infrared component, a transparent original such as a negative or positive original transmits the infrared component regardless of the image (photosensitive image), and an image of dirt, a scratch, or the like which physically shields the optical path is projected as a shadow on the CCD  106 . Hence, the dirt or scratch can be accurately detected.  
         [0038]    Image processing is done for both the obtained dirt/dust-detected image and transparent original-read image. A defective region owing to the dirt or scratch recognized on the dirt/dust-detected image is interpolated from its ambient original-read image. Accordingly, a high-quality transparent original image free from the influence of the dirt or scratch can be read.  
         [0039]    In the first embodiment, dirt or a scratch on a transparent original is read. It is also possible that defect information of all dirt, scratches, and the like present on an optical path extending from the light guide plate to the CCD is read by the above-described method in addition to dirt or a scratch present on an original, thereby excluding the influence.  
         [0040]    (Second Embodiment)  
         [0041]    [0041]FIG. 6 is a schematic perspective view showing the transparent original unit of an image reading apparatus according to the second embodiment of the present invention. In the second embodiment, transparent original reading lamps  6  and dirt/scratch detection lamps  7  are arranged on a light guide plate  19  along different sides of the light guide plate  19  that are perpendicular to each other.  
         [0042]    The transparent original reading lamps  6  are arranged along the long sides of the rectangular light guide plate  19 , whereas the dirt/scratch detection lamps  7  are arranged along the short sides.  
         [0043]    Even with this arrangement, a high-quality transparent original image free from any dirt or scratch can be read.  
         [0044]    As has been described above, according to the above embodiments, the image reading apparatus using a surface light source can attain a high-quality read image free from any dirt or scratch.  
         [0045]    The above embodiments have exemplified a transparent original, but the present invention may be applied to a reflection original. Invisible light may be ultraviolet rays other than infrared rays. The second information may be watermark information other than dirt or a scratch.  
         [0046]    The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, to apprise the public of the scope of the present invention the following claims are made.