Abstract:
A light guide member illuminates with uniform light intensity distribution using the point light source light. On the lower end of the light guide member having a pair of side faces disposed oppositely, a groove is provided for receiving light output from each point light source and diffusing the above received light to at least three directions from the incident side toward the output side. Light components having directions using side-face reflection are generated in the light guide member, enabling light output to multiple directions from the cylindrical-shaped light guide member, and uniform illumination over a wide range. By using the ring-shaped light guide member, cost reduction is effectively achieved, and miniaturization of the illumination mechanism and the image capturing mechanism can also be attained.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2006-058087, filed on Mar. 3, 2006, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a light guide member and an illumination apparatus for guiding light emitted from a plurality of light-emitting devices to an object, and irradiating the object, and an image capturing apparatus for capturing an image of the object using the same, and more particularly a light guide member and an illumination apparatus for uniformly irradiating a predetermined range of the object with light emitted from a plurality of light-emitting devices functioning as point light sources, and an image capturing apparatus using the same. 
     2. Description of the Related Art 
     An image capturing apparatus for capturing an image in a predetermined range of an object by irradiating the object with uniform light is widely used. In an image processing system using an image captured by such the image capturing apparatus, a sharp image is particularly required. 
     For example, with the development of biometric technologies in recent years, there have been provided a variety of apparatuses for personal identification, which captures an image of a portion of a human body by which an individual can be distinguished and recognizes a feature of the human body, for example, fingerprints of limbs, eye retinas, face and blood vessels. 
     In particular, blood vessels and skin patterns of a palm and a finger are suitable for reliable personal authentication, because a relatively large amount of personal feature data may be obtained therefrom. Further, it is believed that the patterns of blood vessels (veins) do not change from the time of an embryo throughout the lifetime of any person, and that no identical pattern exists among any persons without exception, which are therefore suitable for personal authentication.  FIGS. 19 through 22  show explanation diagrams of the conventional blood vessel image authentication technique. As shown in  FIG. 19 , at the time of registration or authentication, a user puts a palm of a hand  110  close to an image capturing apparatus  100 . The image capturing apparatus  100  emits a near infrared ray, and irradiates the palm of the hand  110 . The image capturing apparatus  100  receives the near infrared ray reflected from the palm of the hand  110  by a sensor. 
     As shown in  FIG. 20 , hemoglobin in the red corpuscle flowing in a vein loses oxygen. Such the hemoglobin (deoxidized hemoglobin) absorbs the near infrared of the vicinity of 760 nm in wavelength. Accordingly, when the palm is irradiated with the near infrared, reflection is reduced in a portion in which a vein exists. Thus, by the degree of strength of the reflected near infrared, the location of veins can be recognized. 
     As shown in  FIG. 19 , first, the user registers a vein image data of the own palm into a server or a card, using the image capturing apparatus  100  shown in  FIG. 19 . Next, to perform personal authentication, the user makes the vein image data of the own palm to be read, using the image capturing apparatus  100  shown in  FIG. 19 . 
     The personal authentication is performed by collating the registered vein image data, which is extracted using a user ID, with a vein pattern in the collation vein image being read above. For example, in the case of the collation of the vein patterns between the registered image and the collation image as shown in  FIG. 21 , the person is authenticated as genuine. Meanwhile, in the case of the collation of the vein patterns between the registered image and the collation image as shown in  FIG. 22 , the person is not authenticated as genuine (see Japanese Unexamined Patent Publication No. 2004-062826, FIGS. 2-9). 
     For such the biometric authentication or the like, it is necessary to image an object (a portion of a human body in case of the biometric authentication) in a non-contact manner. For this purpose, the image capturing apparatus  100  emits light producing uniform light intensity in a certain image capturing range (distance and area), receives the reflected light of the above image capturing range by a sensor, and outputs a captured image signal as an electric signal. 
       FIGS. 23 and 24  show explanation diagrams of the conventional image capturing apparatus. As shown in  FIGS. 23 and 24 , the image capturing apparatus  100  includes an imaging unit  120  at the center, and in the periphery thereof, a plurality of light-emitting devices  130 - 1  to  130 - 8 . The dotted lines shown in  FIG. 23  represent the range of the light having uniform intensity emitted from an individual light-emitting device among the plurality of light-emitting devices  130 - 1  to  130 - 8 . 
     As such, by disposing a plurality of (here, eight) point light sources in the periphery of imaging unit  120 , the imaging range of the imaging unit  120  can be irradiated with the light of uniform intensity. Meanwhile, imaging unit  120  includes a photoelectric conversion unit  122  such as a CMOS sensor, and an optical system  124  such as a lens. Since the photoelectric conversion device, which is a plane photodetector device, has a predetermined light receiving area, a predetermined optical distance is required to guide the reflected light of the image capturing range onto the light-receiving plane of the photoelectric conversion device  122 . For this purpose, a lens  124  such as a fisheye lens is disposed between the photoelectric conversion unit  122  and the object, so that an image of the predetermined image capturing range is projected onto the light-receiving plane of photoelectric conversion device  122 . 
     Thus, conventionally, in order to irradiate the object with each point light source element  130 - 1  to  130 - 8  by sharing a predetermined image capturing range, the point light source elements  130 - 1  to  130 - 8  have been disposed apart from each other, as shown in  FIG. 23 . Also, in order to supply the light of predetermined uniform intensity to the imaging range, the point light source elements  130 - 1  to  130 - 8  have been disposed nearer to the object than the photoelectric conversion device  122 , as shown in  FIG. 24  (see International Patent Publication No. WO 2004/088588, FIGS. 1 and 6). 
     Further, there has also been proposed a method for obtaining illumination having spread light to a certain extent by use of a ring-shaped light guide member. According to the above method, a slope notch is provided on the incident side of the ring-shaped light guide member, and light from the point light source is reflected at the slope notch to a spiral direction of the ring, so as to guide the light to the ring spiral direction, and the light is output from an upper face of the ring, and thus a certain range of ring-shaped illumination is produced (see Japanese Unexamined Patent Publication No. 2000-207916, FIGS. 4, 6, 7 and 10). 
     In the above conventional image capturing apparatus, as described earlier, the point light source elements  130 - 1  to  130 - 8  are disposed apart from each other, and nearer to the object than the photoelectric conversion device  122 , as shown in  FIG. 24 . Therefore, it is difficult to miniaturize the image capturing apparatus. Also, there is a restriction when incorporating the image capturing apparatus into equipment. 
     Further, as also shown in  FIG. 24 , the point light source elements  130 - 1  to  130 - 8  and the photoelectric conversion sensor  122  are disposed in different positions in the height direction of the apparatus. Therefore, a printed circuit board  132  for mounting the point light source elements  130 - 1  to  130 - 8  and another printed circuit board  126  for mounting the photoelectric conversion sensor  122  have been provided separately. 
     As a result, the necessity of two printed circuit boards at the minimum has impeded the cost reduction. Also, the need of two printed circuit boards also causes difficulty in miniaturizing the image capturing apparatus. 
     Further, because the conventional ring-shaped light guide member aims at ring-shaped illumination, the point light source is changed into a ring light source only. Therefore, it is not suitable to obtain uniform light intensity over a plane having a certain area of an image capturing range. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a light guide member and an illumination apparatus for performing spread illumination over an image capturing range even when using a point light source, and an image capturing apparatus for a miniaturized structure using the above light guide member and the illumination apparatus. 
     It is another object of the present invention to provide a light guide member and an illumination apparatus for illuminating an imaging range with substantially uniform light intensity distribution even when using a point light source, and an image capturing apparatus for a miniaturized structure using the light guide member and the illumination apparatus. 
     It is still another object of the present invention to provide a light guide member and an illumination apparatus for uniformly illuminating an object even when using a point light source, and an image capturing apparatus for realizing cost reduction using the light guide member and the illumination apparatus. 
     In order to achieve the aforementioned objects, according to the present invention, a light guide member of a cylindrical shape, which introduces light of a point light source from an incident side and outputs from an output side, includes: a lower end portion for introducing the light of the point light source; an upper end portion for outputting the light; and a light guide portion having a pair of side faces and for guiding the light of the point light source from the lower end portion to the upper end portion. And the above-mentioned lower end portion includes a groove portion for receiving the output light of the point light source and diffusing the output light of the point light source to at least three directions from the incident side toward the output side. 
     Further, according to the present invention, an illumination apparatus includes: a cylinder-shaped light guide member; and a plurality of point light sources disposed at intervals on a lower portion of the cylinder-shaped light guide member along the light guide member. The above-mentioned light guide member includes: a lower end portion for introducing the light of the point light source; an upper end portion for outputting the light; and a light guide portion having a pair of side faces and guiding the light of the point light source from the lower end portion to the upper end portion. Further, the lower end portion includes a groove portion for receiving the output light of the point light source and diffusing the output light of the point light source to at least three directions from the incident side toward the output side. 
     Still further, according to the present invention, an image capturing apparatus, which captures an image of an object by illuminating the object and receives reflected light from the object, includes: a circuit board mounted an image sensor for receiving the reflected light; a plurality of light-emitting devices mounted on the circuit board in the peripheral positions of the image sensor; a ring-shaped light guide member for guiding the light emitted from the plurality of light-emitting devices to an image capturing range, and illuminating the image capturing range; and an optical unit accommodated inside a ring of the ring-shaped light guide member, guiding the reflected light on the illuminated object located in the image capturing range to the image sensor. The above light guide member includes: a lower end portion for introducing the light of the point light source; an upper end portion for outputting the light; and a light guide portion having a pair of side faces and guiding the light of the point light source from the lower end portion to the upper end portion. Further, the lower end portion includes a groove portion for receiving the output light of the point light source and diffusing the output light of the point light source to at least three directions from the incident side toward the output side. 
     Further, according to the present invention, preferably, the groove portion includes a polyhedron having at least two slope faces, and one of the slope faces of the polyhedron refracts the output light of the point light source to the side face direction. 
     Further, according to the present invention, preferably, the groove portion includes a flat portion and at least a pair of slope faces each having an opposite inclination direction, and the pair of slope faces refracts the output light of the point light source to the one side face direction and the other side face direction. 
     Further, according to the present invention, preferably, the flat portion area of the groove portion is smaller than each area of the pair of slope face portions. 
     Further, according to the present invention, preferably, the flat portion and the pair of slope face portions respectively have areas corresponding to emission intensity distribution of the point light source. 
     Further, according to the present invention, preferably, the groove portion has a trapezoidal shape. 
     Further, according to the present invention, preferably, the upper end portion includes a slope face which becomes lower toward the outside of the cylinder-shaped light guide member. 
     Further, according to the present invention, preferably, the image sensor captures an image of a portion of a living body. 
     According to the present invention, a groove is provided on the lower end of the light guide member having a pair of side faces disposed oppositely, for receiving light output from the point light source and diffusing the light output from the point light source to at least three directions from the incident side toward the output side. Thus, by generating light components having directions resulting from reflection on the side faces, light to a multiplicity of directions can be output from the cylindrical-shaped light guide member, and thus, uniform illumination can be performed over a wide range. Because the ring-shaped light guide member can sufficiently be prepared simply by means of formation, cost reduction is effectively achieved, and miniaturization of the illumination mechanism and the imaging mechanism can also be attained. 
     Further scopes and features of the present invention will become more apparent by the following description of the embodiments with the accompanied drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a cross-sectional view of an image capturing apparatus according to one embodiment of the present invention. 
         FIG. 2  shows an exploded structural view of the image capturing apparatus shown in  FIG. 1 . 
         FIG. 3  shows a component layout diagram of the circuit board shown in  FIG. 2 . 
         FIG. 4  shows an explanation diagram of the relationship between the light-emitting device and the photodetector device shown in  FIG. 2 . 
         FIG. 5  shows an assembly diagram of the decomposed components shown in  FIG. 2 . 
         FIG. 6  shows a configuration diagram of the external finishing components shown in  FIG. 1 . 
         FIG. 7  shows a configuration diagram of the assembly of the assembled body shown in  FIG. 2 . 
         FIG. 8  shows an outer view of the image capturing apparatus shown in  FIG. 1 . 
         FIG. 9  shows an explanation diagram of the illumination system shown in  FIG. 1 . 
         FIG. 10  shows a configuration diagram of the light guide member and the light-emitting device shown in  FIG. 9 . 
         FIG. 11  shows a relation diagram of the emission intensity distribution of the light-emitting device, and the lower end portion of the light guide member shown in  FIG. 10 . 
         FIG. 12  shows a first operation explanation diagram of the light guide member shown in  FIG. 10 . 
         FIG. 13  shows a second operation explanation diagram of the light guide member shown in  FIG. 10 . 
         FIG. 14  shows a third operation explanation diagram of the light guide member shown in  FIG. 10 . 
         FIG. 15  shows a light intensity distribution diagram using the light guide member shown in  FIG. 10 . 
         FIG. 16  shows a block diagram of a control circuit for the image capturing apparatus shown in  FIG. 1 . 
         FIG. 17  shows an imaging process flowchart of the control circuit shown in  FIG. 16 . 
         FIG. 18  shows an explanation diagram of distance measurement operation using the configuration shown in  FIG. 16 . 
         FIG. 19  shows an explanation diagram of the conventional palm image capturing apparatus. 
         FIG. 20  shows a principle explanation diagram of the conventional palm image capturing apparatus. 
         FIG. 21  shows an explanation diagram of the conventional palm authentication technique. 
         FIG. 22  shows another explanation diagram of the conventional palm authentication technique. 
         FIG. 23  shows an explanation diagram of an illumination configuration in the conventional image capturing apparatus. 
         FIG. 24  shows a configuration diagram of the conventional image capturing apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiment of the present invention is described hereinafter referring to the charts and drawings, in the order of an image capturing apparatus configuration, an illumination mechanism, an image processing configuration, and other embodiments. However, it is to be noted that the scope of the present invention is not limited to the embodiments described below. 
     Image Capturing Apparatus 
       FIG. 1  shows a cross-sectional view of an image capturing apparatus according to one embodiment of the present invention;  FIG. 2  shows an exploded structural view of the image capturing apparatus shown in  FIG. 1 ;  FIG. 3  shows a top plan view of the circuit board shown in  FIGS. 1 ,  2 ;  FIG. 4  shows an operation explanation diagram of a light-emitting device and a photodetector device shown in  FIG. 3 ;  FIG. 5  shows an assembly diagram when the structures shown in  FIG. 2  are assembled;  FIG. 6  shows a configuration diagram of the external case shown in  FIG. 1 ;  FIG. 7  shows a configuration diagram when the assembled body shown in  FIG. 2  is housed in the external case; and  FIG. 8  shows an outer view of the image capturing apparatus shown in  FIG. 1 . 
     Prior to the description of the configuration shown in  FIG. 1 , referring to  FIGS. 2 through 7 , the configuration of each portion illustrated in  FIG. 1  is described. As shown in  FIG. 2 , an image sensor  30  such as a CMOS image sensor and a polarizing plate  32  are disposed at the center of a camera substrate  20 . In the periphery of the image sensor  30  of the camera substrate  20 , a plurality of light-emitting devices  22 ,  24  and photodetector devices  26  are mounted. 
     Describing in more detail with reference to  FIG. 3 , the image sensor  30  is mounted at the center of the camera substrate  20 , and the polarizing plate  32  is pasted upon the image sensor  30 . Along the circle in the periphery of the image sensor  30  of the camera substrate  20 , a plurality of light-emitting devices  22 ,  24  and the photo-detector devices  26  are mounted. 
     Between each the above first light-emitting device  22  and each the second light-emitting device  24 , the photo-detector device (photodiode)  26  is disposed. As shown in  FIG. 4 , the above photodetector device  26  is provided for receiving the light from both the first light-emitting device  22  and the light from the second light-emitting device  24  (reflected light from a diffusion plate  44  described later), thereby performing APC (automatic power control) of the first light-emitting device  22  and the second light-emitting device  24 . 
     In the above example, in order to independently perform automatic power control of each the first and second light-emitting device  22 ,  24 , which emits light at individual timing, one photodetector device  26  is disposed between the first light-emitting device  22  and the second light-emitting device  24  so as to receive the light from the first and second light-emitting devices  22 ,  24 . Thus, the number of photodetector devices for APC control can be reduced. 
     Further, at the four corners of the camera substrate  20 , four distance-measuring light-emitting devices  52  are provided for measuring the distance to the object. As shown in  FIG. 3 , the above four distance-measuring light-emitting devices  52  are disposed on the diagonal lines of the camera substrate  20 , at the farthest positions on the diagonal lines so that each distance therebetween becomes farthest. From the distances measured by the above four distance-measuring light-emitting devices  52 , the inclination of the object (here, palm) is detected. 
     In brief, on a single camera substrate  20 , there are provided the illumination systems  22 ,  24 ,  26  and the imaging systems  30 ,  32  for capturing an image of the object, as well as the distance-measuring system  52 . 
     Now, referring back to  FIG. 2 , in the upper direction of the light-emitting devices  22 ,  24  of the camera substrate  20 , there are provided four diffusion plates  44  and four polarizing plates  42 . The above diffusion plates  44  and polarizing plates  42  are pasted onto polarization/diffusion plate holders  46  being attached on the four sides of the camera substrate  20 . Each diffusion plate  44  diffuses, to a certain extent, the emission distribution of the directive light emitted from the first and second light-emitting devices  22 ,  24 . Each polarizing plate  42  converts natural light emitted from the first and second light-emitting devices  22 ,  24  to linearly polarized light. 
     In the upper direction of the four polarizing plates  42 , a ring-shaped light guide member  10  is provided. The light guide member  10  is formed of, for example, resin, and guides the light from the first and second light-emitting devices  22 ,  24  of the camera substrate  20  in the upward direction, so as to irradiate the object with uniform light. To fit the dispositions of the light-emitting devices  22 ,  24  of the camera substrate  20 , the light guide member  10  has a ring-shaped structure. As will be described in  FIG. 9  and after, the light guide member  10  guides the light emitted from the first and second light-emitting devices  22 ,  24  to the upward direction, and irradiates the object with uniform light. 
     Further, an optical unit  34  is attached to the camera substrate  20  on the image sensor  30  disposed in the approximate center of the camera substrate  20 , and inside the ring-shaped light guide member  10 . The optical unit  34  is constituted of a lens optical system such as a converging lens. 
     An aperture  50  is mounted on the distance-measuring light-emitting device  52  of the camera substrate  20 . The aperture  50  shuts off diffusion of light to other directions so as to guide the light emitted from the distance-measuring light-emitting devices  52  to the object direction. 
     Separately from the camera substrate  20 , a control substrate  60  is provided. The control substrate  60  is provided for connecting with the outside, and includes an external connector  62  and a camera connector  64  for connecting with the camera substrate  20 . The above control substrate  60  is disposed on the lower portion of the camera substrate  20 , and electrically connected with the camera substrate  20  using the camera connector  64 . Further, a holder cover  68  is provided for external connector  64 . 
     In such a way, the image sensor  30 , the light-emitting devices  22 ,  24 , the photo-detector devices  26  and the distance-measuring light-emitting devices  52  are mounted on the camera substrate  20 . Also, the polarization/diffusion plate holders  46 , the diffusion plates  44 , the polarizing plates  42 , the apertures  50 , the optical unit  34 , and the light guide members  10  are mounted on the above camera substrate  20 , and thus a camera portion is assembled. To the above camera portion, the control substrate  60  is attached.  FIG. 5  shows a state of the unit after attaching the camera portion and the control substrate  60 . 
     Further, as shown in  FIG. 6 , there are prepared a visible-light cutoff filter plate  76 , a hood  78 , a holder assembly  70  and an external case  74 . By attaching attachment unit shown in  FIG. 5  to the holder assembly  70  shown in  FIG. 6 , and also, by attaching the holder cover  68  shown in  FIG. 2  to the holder assembly  70 , the configuration shown in  FIG. 7  is assembled. 
     The configuration shown in  FIG. 7  is then housed into the external case  74  shown in  FIG. 6 , and by attaching the visible-light cutoff filter plate  76  having an attached hood  78  on the upper portion of the external case  74 , an image capturing apparatus shown in  FIG. 8  is structured. The above visible-light cutoff filter plate  76  cuts off the visible light component so as not to enter the image sensor  30  from outside. Further, as also described in  FIG. 1 , the hood  78  shuts off the light so that the light outside the predetermined image capturing area does not enter the optical unit  34 , and prevents the light being leaked from the light guide member  10  from invading into the optical unit  34 . 
       FIG. 1  shows a cross-sectional view of the finished body  1  shown in  FIG. 8 . As described earlier, the image sensor  30 , the light-emitting devices  22 ,  24 , the photo-detector devices  26  and the distance-measuring light-emitting device  52  are mounted on the camera substrate  20 . Namely, a basic structure including the illumination system and the imaging system is mounted on the single substrate. Accordingly, only one mounting board is sufficient, thus contributing to cost reduction. 
     Also, with the provision of ring-shaped light guide member  10  on the upper portion of the light-emitting devices  22 ,  24 , the light from the light-emitting devices  22 ,  24  is guided to the visible-light filter  76 . The above light guide member  10  separates the light from the light-emitting devices  22 ,  24  and then forwards the light to the visible-light filter  76 . Therefore, the light-emitting devices  22 ,  24  can be disposed close to the image sensor  30 , and also on the identical substrate  20 , which enables miniaturization, and illumination of the object by uniform light as well. More specifically, assuming that an oblique line portion of an upside-down triangle shape shown in  FIG. 1  is the image capturing range of the camera, the image capturing range can be illuminated by uniform light. 
     Further, because the light guide member  10  has a ring shape, it is possible to house the optical unit  34  inside ring  10 , thus enabling further miniaturization. In addition, the hood  78  prevents the light outside the predetermined image capturing range (oblique line portion in  FIG. 1 ) from entering the optical unit  34 , and also prevents the light leaked from the light guide member  10  from invading into the optical unit  34 . Accordingly, even when the light guide member  10  and the light-emitting devices  22 ,  24  are disposed close to the image sensor  30  and optical unit  34 , degradation in imaging accuracy can be avoided. 
     Moreover, since the distance-measuring light-emitting devices  52  are provided on the camera substrate  20 , it becomes possible to further miniaturize the camera unit measuring the distance. Additionally, in  FIG. 1 , the control substrate  60  is connected to the lower portion of the camera substrate  20 , and an external cable  2  is connected to the external connector  62  of the control substrate  60 . 
     Illumination Mechanism 
     Next, an illumination mechanism including a light guide member will be described.  FIG. 9  shows an operation explanation diagram of the light guide member according to one embodiment of the present invention;  FIG. 10  shows a detailed configuration diagram of the illumination mechanism shown in  FIG. 9 ;  FIG. 11  shows an explanation diagram of a trapezoidal notch of the light guide member shown in  FIG. 10 ;  FIGS. 12 through 14  show explanation diagrams of light guiding and diffusion operations of the light guide member shown in  FIG. 10 ; and  FIG. 15  shows a luminance distribution diagram by the illumination. 
     In  FIG. 9 , like parts as shown in  FIGS. 1 and 2  are designated by like reference numerals. As shown in  FIG. 9 , the light guide member  10  guides the light from each light-emitting device  22  and  24 , which is a point light source, to the visible-light filter  76  so as to split the light into three. 
     More specifically, from the light guide member  10 , basically, light A 3  to the direction of the optical unit  34 , light A 2  to the longitudinal direction of the light guide member  10 , and light A 1  to the opposite direction to the optical unit  34  are output. With the provision of the above light guide member  10 , each single point light source  22 ,  24  can behave as if three point light sources exist in the vicinity of the visible-light filter  76 . 
     As shown in  FIG. 10 , the light guide member  10  includes an upper slope face  14 , two side faces  10 - 1 ,  10 - 2 , and a lower trapezoidal groove  12 . The lower trapezoidal portion  12  is positioned opposite to the light-emitting device  22 ,  24  by the intermediary of the polarizing plate  42  and the diffusion plate  44 , and receives the light from the light-emitting device  22 ,  24 . Also, the upper slope face  14  is a slope face of which height is higher on the optical unit  34  side. 
     As shown in  FIG. 11 , an emission intensity distribution B from the light-emitting device  22 ,  24  has a long (strong) circular arc shape in the upward direction. Namely, the intensity of a light component B 1  to the light output direction of the light-emitting device  22 ,  24  (vertical direction of the device) is stronger than the intensity of light components B 2 , B 3  to the directions to both sides. As shown in  FIG. 9 , trapezoidal groove  12  in the light guide member  10  is formed correspondingly to the above intensity distribution B so that the light can basically be regarded as three point light sources on the output side. 
     More specifically, in order to function as three point light sources by the reflection inside the light guide member  10 , the trapezoidal groove  12  is constituted of a flat portion  12   b  for introducing the light component B 1  without refracting, and a pair of slope face portions  12   a ,  12   c  for refracting and introducing the light components B 2 , B 3  on the both sides and having gradients corresponding to the directions of the light components B 2 , B 3 . The above shapes of the trapezoidal groove  12  function to virtually split the light from each point light source  22 ,  24  into three. 
     Also, as described later, the respective lengths of the above flat portion  12   b  and slope face portions  12   a  and  12   c  are set so that the light intensity in a predetermined area caused by the light output from the light guide member  10  becomes substantially uniform. Here, the length of flat portion  12   b , which receives the maximum intensity of the light component B 1 , is set shorter than each length of slope face portions  12   a ,  12   c , which receive light intensity of the light components B 2 , B 3  weaker than the light intensity of the light component B 1 . By this, depending on the light intensity distribution, the split light amount is adjusted. 
     The above operation is described referring to  FIGS. 12 through 14 . As shown in  FIG. 12 , the component B 2  on the left side of the emission intensity distribution B of each light-emitting device  22 ,  24  is refracted at the left slope face portion  12   a  of the light guide member  10 , and incident to the left side face  10 - 2  of the light guide member  10 . The incident light is then reflected on the left side face  10 - 2 , and forwarded to the right side face  10 - 1  of the light guide member  10 . Subsequently, the light forwarded to the right side face  10 - 1  is reflected on the right side face  10 - 1 , and forwarded again to the left side face  10 - 2 . The light is then reflected on the left side face  10 - 2  and the reflected light is incident to the upper slope face  14  substantially perpendicularly, and output to the outermost portion of the image capturing range. 
     Also, as shown in  FIG. 13 , the central component B 1  of the emission intensity distribution B of the light-emitting device  22 ,  24  is incident to the light guide member  10  from the central flat portion  12   b  of the light guide member  10 . The light is then incident obliquely to the upper slope face  14 , and output to the innermost portion of the image capturing range. 
     Further, as shown in  FIG. 14 , the component B 3  on the right side of the emission intensity distribution B of the light-emitting device  22 ,  24  is refracted at the right slope face portion  12   c  of the light guide member  10 , and incident to the right side face  10 - 1  of the light guide member  10 . The incident light is then reflected on the right side face  10 - 1 , and forwarded to the left side face  10 - 2  of the light guide member  10 . Subsequently, the light forwarded to the left side face  10 - 2  is reflected on the left side face  10 - 2  and is incident to the upper slope face  14  substantially perpendicularly, and output between the innermost portion and the outermost portion of the image capturing range. 
     By synthesizing  FIGS. 12 through 14 , an optical path diagram as shown in  FIG. 10  is obtained. Namely, at the trapezoidal groove  12 , the light guide member  10  splits the point emission of the point light source  22 ,  24  into three. Using the reflection on the side faces inside the light guide member  10 , each split light is output in such behavior as three point light sources existent on the output side of the light guide member  10 . 
     In this case, considering the image capturing range (shown by oblique lines) shown in  FIG. 1 , the output direction is adjusted at the upper slope face  14  of the light guide member  10 . Also, in order to obtain substantially uniform light intensity in the image capturing range, the lengths i.e. the incident widths of, or the incident amount to, flat portion  12   b  and slope face portions  12   a ,  12   c  of the trapezoidal groove  12  of the light guide member  10  are adjusted, taking into consideration the emission intensity distribution B of the light-emitting device  22 ,  24  described earlier in  FIG. 11 . 
     Here, to obtain the substantially uniform light intensity, because the emission intensity distribution B of the light-emitting device  22 ,  24  described in  FIG. 11  has stronger light intensity at the center, while weaker light intensity in the periphery, the length of the flat portion  12   b  of the trapezoidal groove  12  is set shorter than each length of slope face portions  12   a ,  12   c . Thus, it is structured that the light portion having strong light intensity is incident not only to the flat portion  12   b , but also to the slope face portions  12   a ,  12   c.    
     Also, using the groove  12  having a trapezoidal shape and the upper slope face  14  of the light guide member  10 , and the reflection by the light guide member  10 , the reflected light and the rectilinear light can be output with diffusion so as to obtain substantially uniform light intensity throughout the image capturing range. 
       FIG. 15  shows a diagram illustrating an experiment result in regard to the image capturing range and the light intensity of the image capturing apparatus shown in  FIG. 1 . In  FIG. 15 , the horizontal axis indicates the position, while the vertical axis indicates the light intensity. More specifically, the position is a dot position of image sensor  30 , and here, the image sensor  30  having 640 dots in width is employed. By placing plain white paper for experimental purpose on the flat portion of the upper part of the image capturing range (oblique line portion) shown in  FIG. 1 , thereby producing uniform reflection, an output level value of each dot of the image sensor  30  has been measured. Because of the white paper, the output level value corresponds to the light intensity. 
     According to the above example of the experiment result, substantially uniform light intensity has been obtained in the width of approximately 310 dots in the center of image sensor  30 . For example, the maximum level in the 310 dot width is ‘190’, the minimum level is ‘160’, which range within ±15% of the medium value ‘175’, with the error of 10% or less. 
     Referring to  FIG. 1 , for an image capturing range V of the image sensor  30 , the range of uniform light intensity is shown by V 1 . Although the image capturing range is V, by extracting particularly important features of an imaging object from an image in the range of the above V 1 , highly accurate feature extraction becomes obtainable. 
     In addition, an image obtained outside the range of V 1  may also be used for feature extraction of a lower degree of importance, by matching the level through level correction. 
     Image Processing Configuration 
       FIG. 16  shows a block diagram of an captured image processing apparatus according to one embodiment of the present invention.  FIG. 17  shows a flowchart of the captured image processing in the above image processing apparatus. Also,  FIG. 18  shows an explanation diagram of distance measurement operation. 
     As shown in  FIG. 16 , a drive/process system in the image capturing apparatus includes a first illumination LED driver  94  for driving the first light-emitting device  22 , a second illumination LED driver  96  for driving the second light-emitting device  24 , a distance-measuring LED driver  98  for driving the distance-measuring light-emitting devices  52 , an analog/digital converter  92  for converting the analog output of each pixel from the image sensor  30  to a digital value, and a microcontroller  90 . 
     As described in  FIG. 4 , the first and second illumination LED drivers  94 ,  96  perform APC (automatic power control) in each light emission period, according to the light intensity received in the photo-detector device  26 . Microcontroller (MCU)  90  includes MPU (microprocessor), ROM (read-only memory) and RAM (random access memory), and executes processing including distance measurement  90 A, posture discrimination  90 B, shutter control  90 C and image processing  90 D. 
     Referring to  FIG. 17 , imaging processing in MCU  90  is described below. 
     (S 10 ) MCU  90  drives the distance-measuring light-emitting devices (LED)  52  via the distance-measuring LED driver  98 . By this, four distance-measuring light-emitting devices  52  described in  FIGS. 2 and 3  emit light. As shown in  FIG. 1 , the image sensor  30  photographs an image in the image capturing range. Here, since the illumination light-emitting devices  22 ,  24  are not driven, the image sensor  30  receives only the reflected light from the object in the image capturing range corresponding to the light emitted from the distance-measuring light-emitting devices  52 . In  FIG. 18 , there are shown the positions of the reflected light  52 A,  52 B,  52 C and  52 D in an image  30 A of the image sensor  30 , being received from the object in the image capturing range corresponding to the light emitted from each distance-measuring light-emitting device  52 . The above positions deviate depending on the inclination of the object (for example, palm). 
     (S 12 ) Next, by means of analog/digital (A/D) converter  92 , each analog light reception amount in image  30 A of the image sensor  30  is converted into a digital value, and then stored into the memory of MCU  90 . MCU  90  searches the image data in the memory, and detects the positions of the above reflected light  52 A,  52 B,  52 C and  52 D. 
     At this time, since the four distance-measuring light-emitting devices  52  are disposed diagonally from the center of the image (imaging range) as shown in  FIGS. 3 and 18 , by searching on the straight lines, as shown by the dotted lines in  FIG. 18 , the positions of the four points can be detected from the pixel luminance on the straight lines. Further, because the light-emitting devices  52  are disposed in the farthest positions on the diagonal lines with sufficient distances, it is possible to detect the positions farthest from the center in the image. From the above four positions, MCU  90  detects the distance and the inclination of the object using the triangulation measuring method. Namely, by use of the positions from the center of the image sensor  30 , a distance at each of the four points is calculated, and the inclination (in four directions) can be detected from the distance difference of the four points. 
     (S 14 ) MCU  90  decides whether the distance to the imaging object is appropriate (whether the object is positioned in the image capturing range with a predetermined focal distance). When the distance to the imaging object is not appropriate, MCU  90  displays a guidance message on a non-illustrated display portion. For example, a guidance message of “Put the object (palm) closer.” or “Put the object (palm) further.” is displayed. 
     (S 16 ) When the distance is appropriate, MCU  90  decides whether the inclination of the imaging object is appropriate. For example, when imaging a flat portion (palm, etc.) of the object, it is decided whether the inclination is within a tolerable range. When the inclination of the imaging object is not appropriate, MCU  90  displays a guidance message on the non-illustrated display portion. For example, in case that a palm is the object, a guidance message of “Open your hand.” or the like is displayed. 
     (S 18 ) When the inclination is appropriate, MCU  90  instructs illumination LED drivers  94 ,  96  to emit light. Thus, light-emitting devices  22 ,  24  emit light, so as to irradiate the object. Subsequently, MCU  90  drives a non-illustrated electric shutter (provided in the optical unit), and photographs the image in the image capturing range by the imaging sensor  30 . MCU  90  then stores the image into the memory via A/D converter  92 . Then, the feature is extracted from the above image. 
     As such, the image sensor  30  is also used for the distance-measuring photodetector portion to detect whether the imaging object lies at the focal distance, or the inclination thereof. Thus, in the distance measurement mechanism, it is sufficient to provide the distance-measuring light-emitting devices  52  without particularly providing photodetector devices for distance measurement. This contributes a reduction of cost, and miniaturization as well, due to a reduced number of mounting components. 
     Also, because four distance-measuring light-emitting devices  52  are disposed diagonally from the center of the image (imaging range), the positions of the four points can be detected by searching the image data stored in the memory as shown by the dotted lines in  FIG. 18 , and thus, detection processing becomes easy. Further, because the distance-measuring light-emitting devices  52  are disposed in the furthest positions on the diagonal lines with sufficient distances, it is possible to detect the farthest positions in the image from the center even the apparatus is miniaturized, and detection of the inclination can be performed accurately. 
     Other Embodiments 
     In the aforementioned embodiment, the description is made using the lower groove  12  of a trapezoidal shape. However, other polyhedron shapes are applicable. For example, in the above description, the groove has three planes because of the trapezoidal cross section, but a groove of a polyhedron shape such as having four planes may be used depending on required performance. When attaching importance to the cost, a polyhedron having a smaller number of faces is better, and therefore, a trapezoid is better here. 
     Also, in the above description, the imaging object is exemplified by the palm, and the image processing of the imaging object is exemplified by the vein pattern authentication. However, the present invention is also applicable to other biometric authentication by use of other features of human bodies, including hand skin pattern, blood vessel image of the back of hand, blood vessel image of a finger, and features of face and iris, etc. Also, the present invention is not limited to the application to the biometric authentication, but applicable to other applications. 
     The number of distance-measuring light-emitting devices is not limited to four, but any plurality may be chosen. 
     The foregoing description of the embodiments is not intended to limit the invention to the particular details of the examples illustrated. Any suitable modification and equivalents may be resorted to the scope of the invention. 
     All features and advantages of the invention which fall within the scope of the invention are covered by the appended claims.