Abstract:
This invention has an object of reading a high-quality image by detecting and correcting dust or scratches present on a transparent original in an image reading apparatus for reading, e.g., a transparent original. To achieve this object, an original illumination unit in the image reading apparatus for reading an original includes at least a first light source for emitting light in a visible region, a second light source for emitting light in a n invisible region, and a light guide plate which has these light sources arranged at end faces and has first and second light guide patterns for guiding light beams from the first and second light sources to the entire light-emitting surface.

Description:
FIELD OF THE INVENTION 
   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 
   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. 1A and 1B . 
     FIG. 1A  is a sectional view showing an image reading apparatus, and  FIG. 1B  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 setting 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. 
   The platen glass  702  is an original table for setting a transparent original such as a photographic film. A transparent original set 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 . 
   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. 
   If, however, dirt such as dust exists on a transparent original or an original 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 
   The present invention has been made to solve the above problem, and has as its object to obtain a high-efficiency surface illumination apparatus and attain a high-quality read image from which dust or scratches are effectively removed in an image reading apparatus using the surface light source. 
   To solve the above problem and achieve the above object, an image reading apparatus according to the first aspect of the present invention has the following arrangement. 
   More specifically, an image reading apparatus comprises a first light source for emitting light in a visible region, a second light source for emitting light in an invisible region, a light guide plate which has the first and second light sources arranged at end faces, and has a first light guide pattern for guiding light emitted by the first light source to an entire light-emitting surface and a second light guide pattern for guiding light emitted by the second light source to the entire light-emitting surface, and reading means for converting light from an original illuminated by light which is emitted by the first or second light source and guided by the light guide plate into an image signal. 
   An illumination apparatus according to the first aspect of the present invention has the following arrangement. 
   More specifically, an illumination apparatus comprises a first light source for emitting light in a visible region, a second light source for emitting light in an invisible region, and a light guide plate which has the first and second light sources arranged at end faces, and has a first light guide pattern for guiding light emitted by the first light source to an entire light-emitting surface and a second light guide pattern for guiding light emitted by the second light source to the entire light-emitting surface. 
   An image reading apparatus according to the second aspect of the present invention has the following arrangement. 
   More specifically, an image reading apparatus comprises a first light source for emitting light in a visible region, a second light source constituted by aligning on a light-emitting element substrate a plurality of light-emitting elements for emitting light in an invisible region, a light guide plate for guiding light beams emitted by the first and second light sources through a surface to illuminate an original, and reading means for converting light from the original illuminated by light which is emitted by the first or second light source and guided by the light guide plate into an image signal. 
   An illumination apparatus according to the second aspect of the present invention has the following arrangement. 
   More specifically, an illumination apparatus comprises a first light source for emitting light in a visible region, a second light source constituted by aligning on a light-emitting element substrate a plurality of light-emitting elements for emitting light in an invisible region, and a light guide plate which has the first and second light sources arranged at end faces, and guides incident light beams from the end faces through a surface to substantially uniformly emit light. 
   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 
       FIGS. 1A and 1B  are a schematic sectional view and perspective view, respectively, showing a conventional image reading apparatus; 
       FIG. 2  is a block diagram showing the arrangement of an image reading apparatus according to the first embodiment; 
       FIG. 3  is a schematic perspective view showing the image reading apparatus according to the first embodiment; 
       FIG. 4  is a schematic perspective view showing a transmission illumination unit according to the first embodiment; 
       FIG. 5  is a schematic plan view showing the transmission illumination unit according to the first embodiment; 
       FIG. 6  is a schematic sectional view showing the transmission illumination unit according to the first embodiment; 
       FIG. 7  is a schematic sectional view showing the image reading apparatus according to the first embodiment; 
       FIG. 8  is a block diagram showing the arrangement of an image reading apparatus according to the second embodiment; 
       FIG. 9  is a schematic perspective view showing the image reading apparatus according to the second embodiment; 
       FIG. 10  is a schematic perspective view showing a transmission illumination unit according to the second embodiment; 
       FIG. 11  is a schematic sectional view showing the transmission illumination unit according to the second embodiment; and 
       FIG. 12  is a schematic sectional view showing the transmission illumination unit according to the second embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. 
   (First Embodiment) 
   An image reading apparatus in the first embodiment of the present invention will be described with reference to  FIGS. 2 to 6 . 
     FIG. 2  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. 2 . 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 . 
   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 . 
   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 implemented by a general-purpose random access memory. 
   Reference numeral  31  denotes an interface for communicating with the host  21 . In the first embodiment, the interface  31  is implemented 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 the first embodiment, the offset RAM  32  is implemented by a general-purpose random access memory. 
   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 system 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. 
     FIG. 3  is a schematic perspective view showing the image reading apparatus according to the first embodiment. As shown in  FIG. 3 , 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  via hinges  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. 
   The main body of the image reading apparatus  1  is equipped with a platen glass  13  for setting an original to be read. To read a photographic film, a light-shielding sheet  4  is set on the platen glass  13 . A shading window  4   a  of the light-shielding sheet  4  is to measure shading, and a transparent original setting portion  4   b  is a location where a transparent original is set. 
     FIG. 4  is a schematic perspective view showing the transmission illumination unit  2 .  FIGS. 5 and 6  are a schematic plan view and sectional view, respectively, 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 dust/scratch detection LED substrates  7  formed from infrared LED chips having an emission intensity in only the infrared region. The transparent original reading lamps  6  and dust/scratch detection LED substrates  7  are arranged on different sides of the light guide plate  19  perpendicular to each other. The transparent original reading lamps  6  are disposed on long sides of the light guide plate  19  so as to improve the surface luminance in the visible region. 
   The light guide plate  19  is a resin light guide diffusion panel comprised of a first light guide pattern  21  formed on a surface opposite to the light-emitting surface so as to guide light to the entire light-emitting surface by a plurality of grooves extending in a direction perpendicular to the transparent original reading lamp  6 , a second light guide pattern  22  formed on a surface opposite to the light-emitting surface so as to guide light to the entire light-emitting surface by a plurality of grooves extending in a direction perpendicular to the dust/scratch detection LED substrate  7 , a light guide portion  11  for guiding illumination light L by internal reflection, a reflecting 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 reflecting sheet  10  uniform. 
   Light L emitted by the transparent original reading lamps  6  and dust/scratch detection LED substrates  7  propagates through the light guide portion  11  in the two-dimensional longitudinal direction while being reflected between the reflecting 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. 
     FIG. 7  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 reflecting 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. 
   Transparent original reading operation will be described. 
   The reflecting original illumination lamp  20  and dust/scratch detection LED substrates  7  are turned off, and the transparent original lamps  6  are turned on. Then, the whole surface light source  3  emits light. The carriage  9  is moved in the subscanning direction to project image information on a transparent original onto the CCD  106  via the reflecting mirror  16  and lens  105 . 
   The reflecting original illumination lamp  20  and transparent original illumination lamps  6  are turned off, and the dust/scratch detection LED substrates are turned on. Then, the whole surface light source  3  emits light. The carriage  9  is moved in the subscanning direction to project dust, a scratch, or the like on the transparent original onto the CCD  106  via the reflecting mirror  16  and lens  105 . Since light from the dust/scratch detection LED substrate contains only infrared components, the transparent original such as a negative or positive film transmits the infrared components regardless of the image (photosensitive image). An image of dust, a scratch, or the like which physically intercepts the optical path is projected as a shadow on the CCD  106 . The dust or scratch can be accurately detected. 
   Both the dust/scratch detection image and the read image of the transparent original undergo image processing. The defective region having the dust or scratch recognized on the dust/scratch detection image is interpolated from the ambient original-read image. A high-quality transparent original image free from the influence of the dust or scratch can be read. 
   Although the invisible light source emits infrared rays in the above description, the use of ultraviolet rays enables processing an image in the ultraviolet region. A transparent original such as a film has been exemplified as an original. The present invention can also be applied to a reflecting original. 
   As described above, the first embodiment can provide a surface illumination apparatus with high emission efficiency. The image reading apparatus using the surface light source can attain a high-quality read image from which dust or scratches are effectively removed. 
   (Second Embodiment) 
   An image reading apparatus in the second embodiment of the present invention will be described with reference to  FIGS. 8 to 12 . 
   The internal block arrangement of the image reading apparatus in the second embodiment shown in  FIG. 8  is the same as that of the image reading apparatus in the first embodiment shown in  FIG. 2  except for a light source  203 , and a repetitive description thereof will be omitted. 
     FIG. 9  is a schematic perspective view showing the image reading apparatus according to the second embodiment. The arrangement shown in  FIG. 9  is also the same as the first embodiment shown in  FIG. 3  except for the light source  203 , and a description thereof will be omitted. 
     FIG. 10  is a schematic perspective view showing a transmission illumination unit  2  according to the second embodiment.  FIG. 11  is a sectional view showing the surface light source  203 . The surface light source  203  is constructed by a light guide plate  219 , transparent original reading lamps  206  such as fluorescent tubes or xenon lamps, and dust/scratch detection LED substrates  207  having an emission intensity in only the infrared region. The transparent original reading lamps  206  and dust/scratch detection LED substrates  207  are arranged on different sides of the light guide plate  219  perpendicular to each other. 
   Each dust/scratch detection LED substrate  207  is formed from a plurality of infrared LED chips  207   a  and an LED substrate  207   b  having light-emitting apertures  207   c  at positions corresponding to the infrared LED chips  207   a . The infrared LED chip  207   a  is arranged such that the light-emitting portion of the infrared LED chip  207   a  is fit in the light-emitting aperture  207   c  of the LED substrate  207   b  from a side opposite to the light guide facing surface of the LED substrate  207   b . The light guide facing surface of the LED substrate  207   b  is flat. The light guide facing surface of the LED substrate  207   b  is printed in white, which allows efficiently reflecting light. This can increase the luminance of the entire surface light source  203 . 
   Each dust/scratch detection LED substrate  207  is tightly fixed to an end face of the light guide plate  219  by covering the substrate  207  with a reflecting sheet  210  bent at predetermined positions of the light guide  219 , as shown in  FIG. 11 . Infrared rays can be efficiently guided to the light guide. 
   The light guide plate  219  is a resin light guide diffusion panel constituted by a light guide portion  211  for guiding illumination light L in the two-dimensional longitudinal direction by internal reflection, the reflecting sheet  210  for reflecting in the original direction the light guided by the light guide portion  211 , and a diffusion sheet  212  for making the light reflected by the reflecting sheet  210  uniform. 
   Light L emitted by the transparent original reading lamps  206  and dust/scratch detection LED substrates  207  propagates through the light guide portion  211  in the two-dimensional longitudinal direction while being reflected between the reflecting sheet  210  and the diffusion sheet  212 . Part of the light incident on the diffusion sheet  212  diffuses, and the entire surface of the light guide plate  219  emits light. 
   The reflecting sheet  210  at the end of the light-emitting surface of the light guide is extended close to the image reading region so as to prevent light from the LED from directly entering the image reading region. The entire surface of the light guide  219  can more uniformly emit light. 
     FIG. 12  is a sectional view showing the image reading apparatus according to the second embodiment. A carriage  9  of an image reading apparatus  1  supports a reflecting original illumination lamp  20 , a CCD line sensor  106 , a lens  105 , and a reflecting mirror  16 . The CCD line sensor  106  converts an image into an electrical 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. 
   Transparent original reading operation will be described. 
   The reflecting original illumination lamp  20  and dust/scratch detection LED substrates  207  are turned off, and the transparent original lamps  206  are turned on. Then, the whole surface light source  203  emits light. The carriage  9  is moved in the subscanning direction to project image information on a transparent original onto the CCD  106  via the reflecting mirror  16  and lens  105 . 
   The reflecting original illumination lamp  20  and transparent original illumination lamps  206  are turned off, and the dust/scratch detection LED substrates are turned on. Then, the whole surface light source  3  emits light. The carriage  9  is moved in the subscanning direction to project dust, a scratch, or the like on the transparent original onto the CCD  106  via the reflecting mirror  16  and lens  105 . Since light from the dust/scratch detection LED substrate contains only infrared components, the transparent original such as a negative or positive film transmits the infrared components regardless of the image (photosensitive image). An image of dust, a scratch, or the like which physically intercepts the optical path is projected as a shadow on the CCD  106 . The dust or scratch can be accurately detected. 
   Both the dust/scratch detection image and the read image of the transparent original undergo image processing. The defective region having the dust or scratch recognized on the dust/scratch detection image is interpolated from the ambient original-read image. A high-quality transparent original image free from the influence of the dust or scratch can be read. 
   Although the invisible light source emits infrared rays in the above description, the use of ultraviolet rays enables processing an image in the ultraviolet region. The present invention is not limited to a transparent original reading apparatus, but can also be applied to a reflecting original reading apparatus. 
   As described above, the second embodiment can implement a high-efficiency surface illumination apparatus. The image reading apparatus using the surface light source can obtain a high-quality read image free from any dust or scratches. 
   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.