Patent Publication Number: US-8979741-B2

Title: Endoscopic apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of PCT/JP2007/056088 filed on Mar. 23, 2007 and claims benefit of Japanese Application No. 2006-110187 filed in Japan on Apr. 12, 2006, the entire contents of which are incorporated herein by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an endoscopic apparatus and, more particularly, to an endoscopic apparatus capable of imaging an internal portion of a living body by means of a narrow band light. 
     2. Description of the Related Art 
     Endoscopic apparatuses having an endoscope, a light source device and other components have been widely used in the field of medical treatment or the like. In particular, endoscopic apparatuses in the field of medical treatment are applied mainly to uses in which an operator or the like performs imaging or the like of an internal portion of a living body. 
     Instances of imaging with an endoscopic apparatus generally known in the field of medical treatment include normal imaging that is performed by irradiating a subject in a living body with white light, and that enables obtaining generally the same image of the subject as one observed with the naked eye, and imaging with a narrow band light (narrow band imaging (NBI)) that is performed by irradiating the subject with narrow band light having a band narrower than that of illumination light in the normal imaging, and that thereby enables obtaining an image in which blood vessels and other portions in a mucosal surface layer in a living body are emphasized in comparison with the normal imaging. 
     An endoscopic apparatus proposed in Japanese Patent Application Laid-Open Publication No. 2002-095635 is configured of a light source device provided with a filter having discrete spectral characteristics for outputting a narrow band illumination light, and an endoscope for picking up an image of a subject illuminated with the illumination light. The endoscopic system proposed in Japanese Patent Application Laid-Open Publication No. 2002-095635 has the above-described configuration and is therefore capable of narrow band imaging of the subject. 
     SUMMARY OF THE INVENTION 
     An endoscopic apparatus according to a first aspect of the present invention includes an illumination unit capable of emitting to a subject in a living body first narrow band light having a wavelength band in a blue region and second narrow band light having a wavelength band in a green region, an image pickup unit of picking up a first subject image when the subject in the living body is illuminated with the first narrow band light, and picking up a second subject image when the subject in the living body is illuminated with the second narrow band light, a storage unit of storing the first subject image as a green component and a blue component, and storing the second subject image as a red component and a blue component, and a color tone conversion unit of performing predetermined color conversion processing on the red component, the green component and the blue component, to form an image of a predetermined object other than living tissues picked up as the first subject image and the second subject image as an image having a predetermined first color other than red. 
     An endoscopic apparatus of a second aspect of the present invention is the endoscopic apparatus according to the first aspect, wherein the predetermined object comprises at least one of a residue, bile and intestinal juice existing in the living body. 
     An endoscopic apparatus of a third aspect of the present invention is the endoscopic apparatus according to the first aspect, wherein the color tone conversion unit performs processing, as the predetermined color conversion processing, on the basis of the second subject image accumulated as the red component, the first subject image accumulated as the green component and the second subject image accumulated as the blue component so that the luminance value of the red component and the luminance value of the blue component in the image of the predetermined object are substantially equal to each other. 
     An endoscopic apparatus of a fourth aspect of the present invention is the endoscopic apparatus according to the second aspect, wherein the color tone conversion unit performs processing, as the predetermined color conversion processing, on the basis of the second subject image accumulated as the red component, the first subject image accumulated as the green component and the second subject image accumulated as the blue component so that the luminance value of the red component and the luminance value of the blue component in the image of the predetermined object are substantially equal to each other. 
     An endoscopic apparatus of a fifth aspect of the present invention is the endoscopic apparatus according to the first aspect, wherein the predetermined first color is magenta. 
     An endoscopic apparatus of a sixth aspect of the present invention is the endoscopic apparatus according to the second aspect, wherein the predetermined first color is magenta. 
     An endoscopic apparatus of a seventh aspect of the present invention is the endoscopic apparatus according to the third aspect, wherein the predetermined first color is magenta. 
     An endoscopic apparatus of an eighth aspect of the present invention is the endoscopic apparatus according to fourth aspect, wherein the predetermined first color is magenta. 
     An endoscopic apparatus of a ninth aspect of the present invention is the endoscopic apparatus according to the first aspect, wherein the color tone conversion unit further performs processing, as the predetermined color conversion processing, on the basis of the second subject image accumulated as the red component, the first subject image accumulated as the green component and the first and second subject images accumulated as the blue component, to form an image of a local portion picked up as the first subject image and the second subject image and having halation therein into as an image having a predetermined second color. 
     An endoscopic apparatus of a tenth aspect of the present invention is the endoscopic apparatus according to the second aspect, wherein the color tone conversion unit further performs processing, as the predetermined color conversion processing, on the basis of the second subject image accumulated as the red component, the first subject image accumulated as the green component and the first and second subject images accumulated as the blue component, to form an image of a local portion picked up as the first subject image and the second subject image and having halation therein as an image having a predetermined second color. 
     An endoscopic apparatus of an eleventh aspect of the present invention is the endoscopic apparatus according to the ninth aspect, wherein the predetermined second color is white. 
     An endoscopic apparatus of a twelfth aspect of the present invention is the endoscopic apparatus according to the tenth aspect, wherein the predetermined second color is white. 
     An endoscopic apparatus of a thirteenth aspect of the present invention is the endoscopic apparatus according to the first aspect, wherein the illumination unit successively emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a fourteenth aspect of the present invention is the endoscopic apparatus according to the second aspect, wherein the illumination unit successively emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a fifteenth aspect of the present invention is the endoscopic apparatus according to the third aspect, wherein the illumination unit successively emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a sixteenth aspect of the present invention is the endoscopic apparatus according to the fourth aspect, wherein the illumination unit successively emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a seventeenth aspect of the present invention is the endoscopic apparatus according to the fifth aspect, wherein the illumination unit successively emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of an eighteenth aspect of the present invention is the endoscopic apparatus according to the sixth aspect, wherein the illumination unit successively emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a nineteenth aspect of the present invention is the endoscopic apparatus according to the seventh aspect, wherein the illumination unit successively emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a twentieth aspect of the present invention is the endoscopic apparatus according to the eighth aspect, wherein the illumination unit successively emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a twenty-first aspect of the present invention is the endoscopic apparatus according to the ninth aspect, wherein the illumination unit successively emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a twenty-second aspect of the present invention is the endoscopic apparatus according to the tenth aspect, wherein the illumination unit successively emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a twenty-third aspect of the present invention is the endoscopic apparatus according to the eleventh aspect, wherein the illumination unit successively emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a twenty-fourth aspect of the present invention is the endoscopic apparatus according to the twelfth aspect, wherein the illumination unit successively emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a twenty-fifth aspect of the present invention is the endoscopic apparatus according to the first aspect, wherein the illumination unit simultaneously emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a twenty-sixth aspect of the present invention is the endoscopic apparatus according to the second aspect, wherein the illumination unit simultaneously emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a twenty-seventh aspect of the present invention is the endoscopic apparatus according to the third aspect, wherein the illumination unit simultaneously emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a twenty-eighth aspect of the present invention is the endoscopic apparatus according to the fourth aspect, wherein the illumination unit simultaneously emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a twenty-ninth aspect of the present invention is the endoscopic apparatus according to the fifth aspect, wherein the illumination unit simultaneously emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a thirtieth aspect of the present invention is the endoscopic apparatus according to the sixth aspect, wherein the illumination unit simultaneously emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a thirty-first aspect of the present invention is the endoscopic apparatus according to the seventh aspect, wherein the illumination unit simultaneously emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a thirty-second aspect of the present invention is the endoscopic apparatus according to the eighth aspect, wherein the illumination unit simultaneously emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a thirty-third aspect of the present invention is the endoscopic apparatus according to the ninth aspect, wherein the illumination unit simultaneously emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a thirty-fourth aspect of the present invention is the endoscopic apparatus according to the tenth aspect, wherein the illumination unit simultaneously emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a thirty-fifth aspect of the present invention is the endoscopic apparatus according to the eleventh aspect, wherein the illumination unit simultaneously emits the first narrow band light and the second narrow band light to the subject. 
     An endoscopic apparatus of a thirty-sixth aspect of the present invention is the endoscopic apparatus according to the twelfth aspect, wherein the illumination unit simultaneously emits the first narrow band light and the second narrow band light to the subject. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing an example of a configuration of essential components of an endoscopic apparatus according to a first embodiment; 
         FIG. 2  is a diagram showing an example of a configuration of a rotary filter in the endoscopic apparatus shown in  FIG. 1 ; 
         FIG. 3  is a diagram showing an example of transmission characteristics of a first group of filters in the rotary filter shown in  FIG. 2 ; 
         FIG. 4  is a diagram showing an example of transmission characteristics of a second group of filters in the rotary filter shown in  FIG. 2 ; 
         FIG. 5  is a diagram showing an example of a configuration of an image processing circuit in the endoscopic apparatus shown in  FIG. 1 ; 
         FIG. 6  is a diagram showing an example of an image of a subject in a narrow band imaging mode obtained by imaging using the endoscopic apparatus shown in  FIG. 1 ; 
         FIG. 7  is a diagram showing an example of a configuration of essential components of an endoscopic apparatus according to a second embodiment; 
         FIG. 8  is a diagram showing an example of spectral characteristics of a narrow band filter provided in the endoscopic apparatus according to the second embodiment; and 
         FIG. 9  is a diagram showing an example of arrangement of filters used in a color separating filter provided in the endoscopic apparatus according to the second embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     (First Embodiment) 
       FIGS. 1 to 6  relate to a first embodiment of the present invention.  FIG. 1  is a diagram showing an example of a configuration of essential components of an endoscopic apparatus according to the first embodiment.  FIG. 2  is a diagram showing an example of a configuration of a rotary filter in the endoscopic apparatus shown in  FIG. 1 .  FIG. 3  is a diagram showing an example of transmission characteristics of a first group of filters in the rotary filter shown in  FIG. 2 .  FIG. 4  is a diagram showing an example of transmission characteristics of a second group of filters in the rotary filter shown in  FIG. 2 .  FIG. 5  is a diagram showing an example of a configuration of an image processing circuit in the endoscopic apparatus shown in  FIG. 1 .  FIG. 6  is a diagram showing an example of an image of a subject in a narrow band imaging mode obtained by imaging using the endoscopic apparatus shown in  FIG. 1 . 
     As shown in  FIG. 1 , the endoscopic apparatus  1  according to the first embodiment is configured essentially of an endoscope  2  which can be inserted in a living body, which picks up an image of a subject such as a living tissue existing in the living body, and which outputs an image of the living tissue as an image pickup signal, a light source device  3  which supplies illumination light for illuminating a subject to the endoscope  2  through a light guide  6 , a video processor  4  which performs signal processing according to the image pickup signal outputted from the endoscope  2  and outputs as a video signal the image pickup signal after the signal processing, and a monitor  5  which displays the image of a subject picked up by the endoscope  2  on the basis of the video signal outputted from the video processor  4 . 
     The endoscope  2  is configured of an illumination optical system  21  through which illumination light supplied from the light source device  3  and transmitted through the light guide  6  is emitted, an objective optical system  22  which forms an image of a subject illuminated with illumination light emitted from the illumination optical system  21 , a CCD (charge-coupled device)  23  disposed at the image forming position of the objective optical system  22 , and an imaging mode change switch  24  which outputs an imaging mode change command signal to the video processor  4  to change imaging modes of the endoscopic apparatus  1 . 
     The CCD  23  as an image pickup unit picks up images of a subject illuminated with illumination light successively emitted from the illumination optical system  21  and outputs the images of the subject as image pickup signals. 
     The imaging mode change switch  24  can be operated by an operator or the like to select one of imaging modes of the endoscopic apparatus  1 : a normal imaging mode in which generally the same image of a subject as the image of the subject observed with the naked eye can be obtained, and a narrow band imaging mode in which images in which blood vessels and other portions in a mucosal surface layer in a living body are emphasized can be obtained. 
     The light source device  3  as an illumination unit has a lamp  31  which is constituted by a xenon lamp or the like, and which emits white light, a heat ray cut filter  32  which blocks heat rays in the white light emitted from the lamp  31 , a diaphragm device  33  which controls the quantity of white light passing through the heat ray cut filter on the basis of a diaphragm control signal outputted from the video processor  4 , a rotary filter  34  which changes white light passing through the diaphragm device  33  into surface-sequential illumination light, and a collective optical system  35  which collects surface-sequential illumination light passing through the rotary filter  34  and supplies the collected surface-sequential illumination light to the light guide  6 . 
     As shown in  FIG. 2 , the rotary filter  34  is configured in the form of a disk having an axis of rotation at its center, and has a first filter group  34 A provided with a plurality of filters formed along a circumferential direction at an inner peripheral position and a second filter group  34 B provided with a plurality of filters formed along a circumferential direction at an outer peripheral position. 
     The first filter group  34 A is configured of an R filter  34   r  which transmits light having a wavelength band in a red region, a G filter  34   g  which transmits light having a wavelength band in a green region, and a B filter  34   b  which transmits light having a wavelength band in a blue region, the filters  34   r ,  34   g , and  34   b  being provided in the circumferential direction at the inner peripheral position in the rotary filter  34 . 
     The R filter  34   r  has such a configuration as to transmit, for example, light from 600 nm to 700 nm as light having a wavelength band in a red region, as shown in  FIG. 3 . The G filter  34   g  has such a configuration as to transmit, for example, light from 500 nm to 600 nm as light having a wavelength band in a green region, as shown in  FIG. 3 . The B filter  34   b  has such a configuration as to transmit, for example, light from 400 mm to 500 nm as light having a wavelength band in a blue region, as shown in  FIG. 3 . 
     The second filter group  34 B is configured of a Bn filter  34   b   1  which transmits narrow band light in a blue region, and a Gn filter  34   g   1  which transmits narrow band light in a green region, the filters  34   b   1  and  34   g   1  being provided in the circumferential direction at the outer peripheral position in the rotary filter  34 . 
     The Bn filter  34   b   1  has such a configuration as to transmit, for example, light of 415 nm ±15 nm as narrow band light in a blue region, as shown in  FIG. 4 . The Gn filter  34   g   1  has such a configuration as to transmit, for example, light of 540 nm ±15 nm as narrow band light in a green region, as shown in  FIG. 4 . 
     In the first embodiment, the second filter group  34 B is not limited to the one configured only of the Bn filter  34   b   1  and the Gn filter  34   g   1 , and may alternatively be configured of, for example, the above-described two filters and another filter which transmits narrow band light in a red region. 
     The light source device  3  further has a rotary filter motor  36  which rotatively drives the rotary filter  34 , a rotary filter control circuit  37  which controls the rotative drive of the rotary filter motor  36  on the basis of an imaging mode change signal outputted from the video processor  4 , and which outputs a sync signal synchronized with the rotation of the rotary filter  34  to the video processor  4 , and a filter change motor  38  which drives on the basis of the imaging mode change signal outputted from the video processor  4 . 
     The filter change motor  38  places on the optical path of the lamp  31  one of the first filter group  34 A and the second filter group  34 B provided in the rotary filter  34 , on the basis of the imaging mode change signal outputted from the video processor  4 . 
     When, for example, the first filter group  34 A is placed on the optical path of the lamp  31 , the above-described configurations of the portions of the light source device  3  enable white light passing through the R filter  34   r , the G filter  34   g  and the B filter  34   b  to be collected as surface-sequential illumination light formed of R (red) light, C (green) light and B (blue) light by the collective optical system  35  and thereafter supplied to the light guide  6 . When, for example, the second filter group  34 B is placed on the optical path of the lamp  31 , white light passing through the Bn filter  34   b   1  and the Gn filter  34   g   1  is collected as surface-sequential illumination light formed of narrow band light in a blue region (hereinafter referred to as Bn light) and narrow band light in a green region (hereinafter referred to as Gn light) by the collective optical system  35  and thereafter supplied to the light guide  6 . 
     The video processor  4  has a CCD driver  41  which drives the CCD  23  provided in the endoscope  2 , an amplifier  42  which amplifies the image pickup signal outputted from the CCD  23 , a processing circuit  43  which performs processing including correlative double sampling and noise removal on the image pickup signal outputted from the amplifier  42 , an A/D converter  44  which converts the image pickup signal outputted from the processing circuit  43  into a digital image signal, and a white balancing circuit  45  which performs white balancing processing on the image signal outputted from the A/D converter  44 . 
     The video processor  4  also has a synchronization circuit  46  which temporarily stores and synchronizes image signals successively outputted from the white balancing circuit  45 , an image processing circuit  47  which reads out a one-frame image signal from the image signals stored in the synchronization circuit  46  and performs matrix conversion processing and gamma correction processing on the one-frame image signal, a D/A converter  48  which converts the image signal outputted from the image processing circuit  47  into an analog video signal and outputs this signal, and a timing generator  49  which outputs a timing signal to each of the above-described sections of the video processor  4  according to the sync signal outputted from the rotary filter control circuit  37  of the light source device  3 . 
     The synchronization circuit  46  is constituted of a selector  46   a  and memories  46   b ,  46   c , and  46   d.    
     The selector  46   a  successively outputs to the memories  46   b ,  46   c , and  46   d  image signals outputted from the white balancing circuit  45  on the basis of the timing signal outputted from the timing generator  49 . 
     In the memories  46   b ,  46   c , and  46   d  as a storage unit, the memory  46   b  is configured as an R-channel memory, the memory  46   c  as a G-channel memory, and the memory  46   d  as a B-channel memory. That is, the image signal inputted to the memory  46   b  is accumulated as a red component; the image signal inputted to the memory  46   c  as a green component; and the image signal inputted to the memory  46   d  as a blue component. 
     The memories  46   b ,  46   c , and  46   d  temporarily store and synchronize the image signals outputted from the selector  46   a  on the basis of the timing signal outputted from the timing generator  49 . 
     The image processing circuit  47  is constituted of a matrix circuit  47 A, and a γ correction circuit  47 B, as shown in  FIG. 5 . The image processing circuit  47  performs image processing according to the normal imaging mode or the narrow band imaging mode on the basis of the imaging mode change signal outputted from an imaging mode change circuit  50  described below. 
     The matrix circuit  47 A as a color tone conversion unit performs matrix conversion processing described below on the one-frame image signal read out from the synchronization circuit  46  and formed of red, green and blue components to convert the color of the subject in the image signal into a color according to the imaging mode, and thereafter outputs the image signal. 
     The γ correction circuit  47 B performs γ correction processing on the image signal having undergone matrix conversion processing by the matrix circuit  47 A, and outputs the processed image signal. 
     The video processor  4  further has the imaging mode change circuit  50 , a light control parameter change circuit  51  and a light control circuit  52 . 
     The imaging mode change circuit  50  outputs, on the basis of the imaging mode change command signal outputted from the endoscope  2 , the imaging mode change signal to make each section of the light source device  3  and the video processor  4  perform the operation according to the imaging mode. 
     The light control parameter change circuit  51  outputs a light control parameter according to the imaging mode on the basis of the imaging mode change signal outputted from the imaging mode change circuit  50 . 
     The light control circuit  52  outputs a diaphragm control signal for brightness control according to the imaging mode to the diaphragm device  33  on the basis of the light control parameter outputted by the light control parameter change circuit  51  and the image pickup signal outputted from the processing circuit  43 . 
     Next, the operation of the endoscopic apparatus  1  will be described. 
     An operator or the like first powers on the components of the endoscopic apparatus  1 , i.e., the endoscope  2 , the light source device  3 , the video processor  4  and the monitor  5  to activate the components. Note that, it is assumed that in the activated state the endoscope  2 , the light source device  3  and the video processor  4  are set in the normal imaging mode. 
     In the case where the video processor  4  is set in the normal imaging mode, the imaging mode change circuit  50  outputs the imaging mode change signal to the filter change motor  38  on the basis of the imaging mode change command signal outputted from the imaging mode change switch  24  so that the first filter group  34 A in the rotary filter  34  is placed on the optical path of the lamp  31 . The imaging mode change circuit  50  also outputs the imaging mode change signal to the light control parameter change circuit  51  on the basis of the imaging mode change command signal outputted from the imaging mode change switch  24  so that a light control parameter suitable for the normal imaging mode is outputted. Further, the imaging mode change circuit  50  outputs the imaging mode change signal to the rotary filter control circuit  37  on the basis of the imaging mode change command signal outputted from the imaging mode change switch  24  so that the rotary filter  34  is rotatively driven at a rotational speed suitable for the normal imaging mode. 
     The light control parameter change circuit  51  then outputs the light control parameter suitable for the normal imaging mode to the light control circuit  52  on the basis of the imaging mode change signal. 
     The light control circuit  52  outputs the diaphragm control signal to the diaphragm device  33  on the basis of the light control parameter outputted from the light control parameter change circuit  51  so that a quantity of illumination light suitable for the normal imaging mode is supplied by the light source device  3 . 
     The light source device  3  supplies surface-sequential illumination light formed of R light, G light and B light to the light guide  6  based on the imaging mode change signals respectively inputted to the diaphragm device  33 , the rotary filter control circuit  37  and the filter change motor  38 . Also, the rotary filter control circuit  37  of the light source device  3  outputs the sync signal synchronized with the rotation of the rotary filter  34  to the video processor  4 . 
     The surface-sequential illumination light formed of R light, G light and B light is emitted to a subject through the light guide  6  and the illumination optical system  21 . 
     An image of the subject illuminated with the surface-sequential illumination light formed of R light, G light and B light is formed by the objective optical system  22 , picked up by the CCD  23  and then outputted as an image pickup signal to the video processor  4 . 
     The image pickup signal outputted to the video processor  4  is amplified by the amplifier  42 , undergoes processing including correlative double sampling and noise removal performed by the processing circuit  43 , and is converted into a digital image signal by the A/D converter  44 . This digital image signal undergoes white balancing processing performed by the white balancing circuit  45 . A one-frame image signal is obtained from the digital image signal by synchronization in the synchronization circuit  46  and is read to the image processing circuit  47 . Next that, in the normal imaging mode, the image signal for the R light subject image is accumulated as a red component in the memory  46   b , the image signal for the G light subject image is accumulated as a green component in the memory  46   c , and the image signal for the B light subject image is accumulated as a blue component in the memory  46   d.    
     When detecting the setting of the video processor  4  in the normal imaging mode on the basis of the imaging mode change signal outputted from the imaging mode change circuit  50 , the image processing circuit  47  performs only γ correction processing in the γ correction circuit  47 B on the image signal read from the synchronization circuit  46  without performing matrix conversion processing, described below, in the matrix circuit  47 A, and outputs the image signal having undergone the γ correction. 
     The image signal outputted from the image processing circuit  47  is converted into an analog video signal by the D/A converter  48  and thereafter outputted to the monitor  5 . 
     As a result of the above-described processing performed in the video processor  4 , an image of the subject which is substantially the same as the image of the subject imaged with the naked eye, is displayed on the monitor  5  as an image of the subject in the normal imaging mode. 
     The operator or the like thereafter operates and moves the endoscope  2  so that the desired subject in a living body is positioned within the field of view of the objective optical system  22  and at a position at which it is illuminated with illumination light emitted from the illumination optical system  21 . In this state, the operator or the like changes the imaging mode of the endoscopic apparatus  1  from the normal imaging mode to the narrow band imaging mode by operating the imaging mode change switch  24 . 
     When the video processor  4  is set in the narrow band imaging mode, the imaging mode change circuit  50  outputs the imaging mode change signal to the filter change motor  38  on the basis of the imaging mode change command signal outputted from the imaging mode change switch  24  so that the second filter group  34 B in the rotary filter  34  is placed on the optical path of the lamp  31 . The imaging mode change circuit  50  also outputs the imaging mode change signal to the light control parameter change circuit  51  on the basis of the imaging mode change command signal outputted from the imaging mode change switch  24  so that a light control parameter suitable for the narrow band imaging mode is outputted. Further, the imaging mode change circuit  50  outputs the imaging mode change signal to the rotary filter control circuit  37  on the basis of the imaging mode change command signal outputted from the imaging mode change switch  24  so that the rotary filter  34  is rotatively driven at a rotational speed suitable for the narrow band imaging mode. 
     The light control parameter change circuit  51  then outputs the light control parameter suitable for the narrow band imaging mode to the light control circuit  52  on the basis of the imaging mode change signal. 
     The light control circuit  52  outputs the diaphragm control signal to the diaphragm device  33  on the basis of the light control parameter outputted from the light control parameter change circuit  51  so that a quantity of illumination light suitable for the narrow band imaging mode is supplied by the light source device  3 . 
     The light source device  3  supplies surface-sequential illumination light formed of Gn light and Bn light to the light guide  6  based on the imaging mode change signals respectively inputted to the diaphragm device  33 , the rotary filter control circuit  37  and the filter change motor  38 . Also, the rotary filter control circuit  37  of the light source device  3  outputs the sync signal synchronized with the rotation of the rotary filter  34  to the video processor  4 . 
     The surface-sequential illumination light formed of Gn light and Bn light is emitted to the subject through the light guide  6  and the illumination optical system  21 . 
     An image of the subject illuminated with the surface-sequential illumination light formed of Gn light and Bn light is formed by the objective optical system  22 , picked up by the CCD  23 , and then outputted as an image pickup signal to the video processor  4 . That is, the CCD  23  picks up a first subject image when the subject is illuminated with Bn light, picks up a second subject image when the subject is illuminated with Gn light, and outputs each subject image as an image pickup signal. 
     The image pickup signal outputted to the video processor  4  is amplified by the amplifier  42 , undergoes processing including correlative double sampling and noise removal performed by the processing circuit  43 , and is converted into a digital image signal by the A/D converter  44 . This digital image signal undergoes white balancing processing performed by the white balancing circuit  45 . A one-frame image signal is obtained from the digital image signal by synchronization in the synchronization circuit  46  and is read to the image processing circuit  47 . In the narrow band imaging mode, the selector  46   a  outputs a G i  signal, which is an image signal for the image of the subject illuminated with Gn light, to the memories  46   b  and  46   d , and outputs a B i  signal, which is an image signal for the image of the subject illuminated with Bn light, to the memories  46   c  and  46   d.    
     When the image processing circuit  47  detects the setting of the video processor  4  in the narrow band imaging mode on the basis of the imaging mode change signal outputted from the imaging mode change circuit  50 , the image processing circuit  47  performs matrix conversion processing as predetermined color conversion processing on each image signal read from the synchronization circuit  46  in the matrix circuit  47 A. 
     The matrix circuit  47 A performs matrix conversion based on the expression (1) shown below, on each of the G i  and B i  signals read from the memories in the synchronization circuit  46  to output an R o  signal, a G o  signal and a B o  signal as red, green and blue components therefrom. 
     
       
         
           
             
               
                 
                   
                     ( 
                     
                       
                         
                           
                             R 
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                             B 
                             o 
                           
                         
                       
                     
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                   = 
                   
                     
                       ( 
                       
                         
                           
                             
                               k 
                               1 
                             
                           
                           
                             0 
                           
                         
                         
                           
                             0 
                           
                           
                             
                               k 
                               2 
                             
                           
                         
                         
                           
                             
                               k 
                               3 
                             
                           
                           
                             0 
                           
                         
                       
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                     ⁢ 
                     
                       ( 
                       
                         
                           
                             Gi 
                           
                         
                         
                           
                             Bi 
                           
                         
                       
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                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     More specifically, the matrix circuit  47 A performs matrix conversion processing based on the expression (1) shown above by multiplying the luminance value of the G i  signal read from the memory  46   b  by k 1  to obtain a signal and outputs this signal as an R o  signal which is a red component after the matrix conversion processing. 
     Also, the matrix circuit  47 A performs matrix conversion processing based on the expression (1) shown above by multiplying the luminance value of the B i  signal read from the memory  46   c  by k 2  to obtain a signal and outputs this signal as a G, signal which is a green component after the matrix conversion processing. 
     Further, the matrix circuit  47 A performs matrix conversion processing based on the expression (1) shown above by multiplying the luminance value of the G i  signal read from the memory  46   d  by k 3  to obtain a signal and outputs this signal as a B o  signal which is a blue component after the matrix conversion processing. 
     In expression (1), it is noted that the constant k 3  is a value smaller than either of the constant k 1  and the constant k 2 . More specifically, it is noted that the values of the constant k 1 , the constant k 2  and the constant k 3  satisfy, for example, a magnitude relationship: k 3 &lt;k 1 &lt;k 2 . 
     The γ correction circuit  47 B performs γ correction processing on the image signals which are outputted from the matrix circuit  47 A, on which matrix conversion processing based on the expression (1) shown above has been performed, and which comprise the R o  signal, G o  signal and B o  signal, and outputs the processed image signals. 
     The image signals outputted from the image processing circuit  47  are converted into analog video signals by the D/A converter  48  and thereafter outputted to the monitor  5 . 
     The above-described sequence of processing is performed in the video processor  4  to display an image of the subject in the narrow band imaging mode on the monitor  5 . For example, as an image of the subject in the narrow band imaging mode, images such as those in  FIG. 6 , i.e., an image in which images of capillaries  101  in the vicinity of a mucosal surface layer in the living body are emphasized, and an image of a residue  102 , as an image of a predetermined object different from living tissues, are displayed on the monitor  5 . Note that, the residue  102  may be any other predetermined object different from living tissues, e.g., bile or intestinal juice. 
     The images of capillaries  101  are displayed, for example, in brown or a color close to the brown as a result of the above-described matrix conversion processing performed in the video processor  4 . Also, the image of residue  102  is displayed, for example, in magenta or a color close to magenta as a result of the above-described matrix conversion processing performed in the video processor  4 . That is, the matrix circuit  47 A performs processing in the above-described matrix conversion processing so that the luminance value of the red component and the luminance value of the blue component in the image of residue  102  are substantially equal to each other. 
     By the above-described function, the endoscopic apparatus  1  in the first embodiment can obtain in narrow band imaging an image in which capillaries in the vicinity of a mucosal surface layer in a living body are emphasized, and can also obtain an image in which an image of a residue has a color different from a red color substantially the same as that of blood. Thus, the endoscopic apparatus  1  in the first embodiment can reduce the burden on an operator or the like in a case where narrow band imaging is performed on a living body. 
     The matrix circuit  47 A in a configuration for obtaining substantially the same effect as that described above is not limited to one for performing matrix conversion processing based on expression (1). For example, the matrix circuit  47 A may be configured to perform matrix conversion processing based on an expression (2) shown below. 
     
       
         
           
             
               
                 
                   
                     ( 
                     
                       
                         
                           
                             R 
                             o 
                           
                         
                       
                       
                         
                           
                             G 
                             o 
                           
                         
                       
                       
                         
                           
                             B 
                             o 
                           
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             
                               k 
                               1 
                             
                           
                           
                             0 
                           
                         
                         
                           
                             0 
                           
                           
                             
                               k 
                               2 
                             
                           
                         
                         
                           
                             
                               k 
                               3 
                             
                           
                           
                             
                               k 
                               4 
                             
                           
                         
                       
                       ) 
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           
                             Gi 
                           
                         
                         
                           
                             Bi 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     The matrix circuit  47 A performs matrix conversion processing based on the expression (2) shown above by multiplying the luminance value of the G i  signal read from the memory  46   b  by k 1  to obtain a signal and outputs this signal as an R o  signal which is a red component after the matrix conversion processing. 
     Also, the matrix circuit  47 A performs matrix conversion processing based on the expression (2) shown above by multiplying the luminance value of the B i  signal read from the memory  46   c  by k 2  to obtain a signal and outputs this signal as a G o  signal which is a green component after the matrix conversion processing. 
     Further, the matrix circuit  47 A performs matrix conversion processing based on the expression (2) shown above by multiplying the luminance value of the G i  signal read from the memory  46   d  by k 3  to obtain a signal, multiplying the luminance value of the B i  signal read from the memory  46   d  by k 4  to obtain a signal, and outputs a signal obtained by adding these signals together as a B o  signal which is a blue component after the matrix conversion processing. 
     Note that, in expression (2), it is noted that the constant k 3  is a value larger than the above-described constant k 3  and smaller than either of the above-described constant k 1  and constant k 2 . More specifically, it is noted that the values of the constant k 1 , constant k 2 , the constant k 3  and constant k 4  satisfy, for example, a magnitude relationship: k 3 &lt;k 4 &lt;k 1 &lt;k 2 . 
     Processing similar to the above-described sequence of processing is performed subsequently in the video processor  4  to display an image of the subject in the narrow band imaging mode on the monitor  5 . 
     When matrix conversion processing based on expression (2) shown above is performed, an image of residue  102  having substantially the same color as that of the image obtained when matrix conversion processing based on expression (1) is performed is displayed on the monitor  5 . Also, when matrix conversion processing based on expression (2) shown above is performed, images of capillaries  101  having improved contrast in comparison with those obtained when matrix conversion processing based on expression (1) is performed are displayed on the monitor  5 . 
     When matrix conversion processing based on expression (1) shown above is performed, there is a possibility of an image of a local portion  103 , such as shown in  FIG. 6 , to be displayed on the monitor  5  as an image in a color extremely close to yellow due to a halation. On the other hand, when matrix conversion processing based on expression (2) shown above is performed, an image of a local portion  103 , such as shown in  FIG. 6 , is displayed on the monitor  5  as an image in white or in a color close to white. 
     The above-described matrix conversion processing based on expression (2) shown above is performed in the matrix circuit  47 A to display on the monitor  5  as an image of the subject in the narrow band imaging mode images of capillaries  101  having improved contrast in comparison with those obtained when matrix conversion processing based on expression (1) is performed, an image of a residue  102  having a color different from a red color substantially the same as that of blood, and an image of a local portion  103  in white or in a color close to white. 
     (Second Embodiment) 
       FIGS. 7 to 9  relate to a second embodiment of the present invention.  FIG. 7  is a diagram showing an example of a configuration of essential components of an endoscopic apparatus according to the second embodiment.  FIG. 8  is a diagram showing an example of spectral characteristics of a narrow band filter provided in the endoscopic apparatus according to the second embodiment.  FIG. 9  is a diagram showing an example of arrangement of filters used in a color separating filter provided in the endoscopic apparatus according to the second embodiment. 
     In the following description, detailed description will not be made of portions having the same configurations as those in the first embodiment. 
     The endoscopic apparatus  201  according to the second embodiment has, as its essential components, as shown in  FIG. 7 , an electronic endoscope (hereinafter referred to simply as “endoscope”)  202  inserted in a body cavity or the like to perform endoscopic inspection, a light source device  203  which supplies illumination light to the endoscope  202 , a video processor  204  which drives an image pickup unit incorporated in the endoscope  202 , and which performs signal processing on signals outputted from the image pickup unit, and a monitor  205  which displays as an endoscopic image an image of a subject picked up by the image pickup unit on the basis of a video signal outputted from the video processor  204 . 
     The endoscope  202  has an elongated insertion portion  207 , an operation portion  208  provided on a rear end of the insertion portion  207 , and a universal cable  209  extending from the operation portion  208 . A light guide connector  211  provided on an end of the universal cable  209  is detachably connected to the light source device  203 . Further, the universal cable  209  is detachably connected by a signal connector provided on an end thereof to the video processor  204 . 
     A light guide  213  for transmitting illumination light is inserted in the insertion portion  207 . When the light guide connector  211  provided on an end of the light guide  213  on the operator&#39;s hand side is connected to the light source device  203 , illumination light from the light source device  203  is supplied to the light guide  213 . 
     In a normal imaging mode, the light source device  203  emits white (visible-region) illumination light as normal illumination light and supplies the white illumination light to the light guide  213 . In a special imaging mode, e.g., a narrow band imaging mode, the light source device  203  emits narrow band illumination light and supplies the narrow band illumination light to the light guide  213 . 
     A command for changing between the normal imaging mode and the narrow band imaging mode can be provided by operating a mode change switch  214   a  provided in the operation portion  208  of the endoscope  202 . In the endoscopic apparatus  201  according to the second embodiment, the operation to provide a command for changing between the normal imaging mode and the narrow band imaging mode is not limited to operating the mode change switch  214   a  provided in the endoscope  202 . For example, a mode change switch  214   b  provided in an operating panel  217  of the video processor  204  may be operated to provide the command, or foot switch or a keyboard not illustrated may be operated to provide the command. 
     A change signal generated by operating the mode change switch  214   a  or the like is inputted to a control circuit  215  in the video processor  204 . This control circuit  215  selectively changes the illumination light supplied from the light source device  203  to the light guide  213  between the normal illumination light and the narrow band illumination light by controlling a filter insertion/removal device  216  according to the change signal. 
     The control circuit  215  also performs control for changing the characteristics of a video signal processing system in the video processor  204  while interlocking this control with control of changing the illumination light supplied from the light source device  203  to the light guide  213 . That is, the video processor  204  can perform signal processings respectively suitable for the normal imaging mode and the narrow band imaging mode by changing the characteristics of the video signal processing system according to the changing command provided by the mode change switch  214   a.    
     The mode change switch  214   b  and an enhancement level change switch  219  for enhancing the sharpness of an image are also provided in the operating panel  217  of the video processor  204 . Signals outputted from the switches  214   b  and  219  are inputted to the control circuit  215 . The mode change switch  214   b  has the same function as that of the mode change switch  214   a.    
     The light source device  203  incorporates a lamp  220  which emits illumination light including light in a visible region. From the illumination light emitted from the lamp  220 , illumination light having substantially the same wavelength band as that of white light is obtained by cutting infrared light with an infrared cutting filter  221 , and thereafter enters a diaphragm  222 . The amount of opening in the diaphragm  222  is adjusted by control performed by a diaphragm drive circuit  223 . A quantity of light according to the amount of opening is permitted to pass through the diaphragm  222 . 
     The filter insertion/removal device  216  configured of a plunger or the like inserts or removes a narrow band filter  224  in the optical path for the illumination light emitted from the lamp  220  (for example, between the diaphragm  222  and a collective lens  225 ) according to the control of the control circuit  215 . 
     On the other hand, the illumination light passing through the diaphragm  222  enters the collective lens  225  by passing through the narrow band filter  224  (in the narrow band imaging mode) or without passing through the narrow band filter  224  (in the normal imaging mode). After being collected by the collective lens  225 , the illumination light is incident on an incidence end surface of the light guide  213  on the operator&#39;s hand side. 
       FIG. 8  is a diagram showing an example of transmittance characteristics of the narrow band filter  224 . The narrow band filter  224  exhibits three-peak characteristics and has, for example, narrow band transmission filter characteristic portions Ra, Ga, and Ba for transmission in narrow bands in red, green and blue wavelength regions. 
     More specifically, the narrow band transmission filter characteristic portions Ra, Ga, and Ba have band-pass characteristics in which the respective center wavelengths are 600 nm, 540 nm and 420 nm and the full widths at half maximum are 20 to 40 nm. 
     Accordingly, when the narrow band filter  224  is placed on the optical path for the illumination light emitted from the lamp  220 , illumination lights which have passed through the narrow band transmission filter characteristic portions Ra, Ga, and Ba in three narrow bands are simultaneously supplied to the light guide  213 . On the contrary, when the narrow band filter  224  is not placed on the optical path for the illumination light emitted from the lamp  220 , white light (in the visible wavelength region) is supplied to the light guide  213 . 
     The illumination light entering the light guide  213  from the light source device  203  side is transmitted through the light guide  213  and is thereafter emitted to outside through an illumination lens  227  attached to an illumination window provided in a distal end portion  226  of the insertion portion  207 , thereby illuminating a surface of a living tissue such as an affected part in a body cavity. 
     An imaging window is provided in the distal end portion  226  at a position adjacent to the illumination window. An objective lens  228  for forming an optical image by means of return light from a living tissue is mounted in the imaging window. A charge-coupled device (abbreviated as CCD)  229  is disposed as a solid-state image pickup element at the image-forming position of the objective lens  228 . The optical image formed by the objective lens  228  is photoelectrically converted by the CCD  229  and thereafter outputted as an image pickup signal. 
     Complementary color filters shown in  FIG. 3 , for example, are mounted on a pixel-by-pixel basis on the image pickup surface of the CCD  229  as a color separating filter  230  for optically separating colors. 
     The complementary color filters have a configuration in which color chips of four colors: magenta (Mg), green (G), cyan (Cy) and yellow (Ye) are disposed in front of CCD elements forming pixels. More specifically, the complementary color filters have a configuration in which Mg and G color chips are alternately disposed in a horizontal direction. The complementary color filters also have a configuration in which a group of color chips repeatedly disposed in order of Mg, Cy, Mg, and Ye, . . . in a vertical direction and another group of color chips repeatedly disposed in order of G, Ye, G, Cy, . . . are alternately disposed. 
     In the case of the CCD  229  using the complementary color filters as color separating filter  230 , pixels in pairs of rows adjacent to each other in the vertical direction are successively read out while being added together. In this reading, the pixels are read by shifting the pairs of rows in correspondence with transition between odd fields and even fields. As is known, a luminance signal and a color signal are produced by processing performed by a Y/C separation circuit  237  in a stage after reading. 
     The CCD  229  is connected to one end of each of signal lines in the endoscope  202 . The signal connector incorporating the other end of each of the signal lines is physically connected to the video processor  204 , to establish electrical connections between a CCD drive circuit  231  and a correlative double sampling circuit (CDS circuit)  232  in the video processor  204 , and the CCD  229 . 
     Each endoscope  202  has an ID generation section  233  which generates identification information (ID) unique to the endoscope  202 . The ID generated in the ID generation section  233  is inputted to the control circuit  215  via the universal cable  209 . 
     The control circuit  215  identifies, on the basis of the input ID, the type of the endoscope  202  connected to the video processor  204 , the type of the CCD  229  mounted in the endoscope  202 , the number of pixels of the CCD  229  and so on. The control circuit  215  controls the CCD drive circuit  231  so that the CCD  229  in the identified endoscope  202  is in a suitably driven state. 
     The CCD  229  performs photoelectric conversion of an optical image formed by the objective lens  228  according to a CCD drive signal from the CCD drive circuit  231 . The image pickup signal for the optical image photoelectrically converted by the CCD  229  is inputted to the CDS circuit  232 . 
     The image pickup signal inputted to the CDS circuit  232  is outputted to an A/D conversion circuit  234  as a baseband signal from which signal components have been extracted, and is converted into a digital signal by the A/D conversion circuit  234 . Simultaneously, the brightness (average luminance of the signal) is detected by a brightness detection circuit  235 . 
     A brightness signal having as information the brightness detected by the brightness detection circuit  235  is inputted to a light control circuit  236  and is thereafter converted into a light control signal having as information a difference from a reference brightness (light control target value). The light control signal is used when the diaphragm drive circuit  223  controls the amount of opening of the diaphragm  222  so that the quantity of illumination light supplied from the light source device  203  to the light guide  213  becomes equal to the quantity of light according to the reference brightness. 
     The digital signal outputted from the A/D conversion circuit  234  is gain-controlled by an automatic gain control circuit (abbreviated as AGC circuit)  238  so that the signal level becomes equal to a predetermined level), and is thereafter inputted to the Y/C separation circuit  237 . The Y/C separation circuit  237  produces a luminance signal Yh (as a color signal C in a broad sense) and line-sequential color difference signals Cr (=2R−G) and Cb (=2B−G) on the basis of the inputted digital signal. 
     The luminance signal Yh outputted from the Y/C separation circuit  237  is inputted to a selector  239  and also to a first low-pass filter (abbreviated as LPF)  241  which limits a passband for the inputted signal. 
     The LPF  241  has a wide passband characteristic corresponding to the luminance signal Yh. The luminance signal Yh is filtered according to the passband characteristic to be inputted as a luminance signal Y 1  to a first matrix circuit  242 . 
     On the other hand, the color difference signals Cr and Cb are inputted to a (line-sequential) synchronization circuit  244  via a second LPF  243  which limits a passband for the inputted signal. 
     At this time, a passband characteristic of the second LPF  243  is changed according to the imaging mode by being controlled by the control circuit  215 . More specifically, the second LPF  243  is controlled by the control circuit  215  to be set so as to have, in the normal imaging mode, a first passband characteristic in which the passband is lower than that of the first LPF  241 . Also, the second LPF  243  is controlled by the control circuit  215  to be set so as to have, in the narrow band imaging mode, a second passband characteristic in which the passband is wider than that in the first passband characteristic and is substantially equal to that of the first LPF  241 . The second LPF  243  forms processing characteristic changing means capable of changing a processing characteristic by limiting the passband with respect to the color difference signals Cr and Cb while interlocking with changing of the imaging mode. 
     The synchronization circuit  244  synchronizes the inputted color difference signals Cr and Cb and outputs these signals to the first matrix circuit  242 . 
     The first matrix circuit  242  produces three primary color signals R 1 , G 1 , and B 1  according to the luminance signal Y 1  and the color difference signals Cr and Cb and outputs the produced three primary color signals R 1 , G 1 , and B 1  to a white balancing circuit  245 . 
     Also, the first matrix circuit  242  is controlled by the control circuit  215  to change the values of matrix coefficients (determining a conversion characteristic) according to the characteristics of the color separating filter  230  of the CCD  229  and the characteristics of the narrow band filter  224 . Thus, the first matrix circuit  242  can produce three primary color signals R 1 , G 1 , and B 1  without color mixing or by eliminating color mixing substantially completely. 
     For example, the characteristics of the color separating filter  230  of the CCD  229  incorporated in the endoscope  202  may vary depending on the endoscope  202  actually connected to the video processor  204 . The control circuit  215  changes the coefficients in the first matrix circuit  242  according to the characteristics of the color separating filter  230  of the CCD  229  actually used by referring to the ID information. In this way, the video processor  204  can be suitably adapted even to different types of image pickup elements actually used. Thus, the occurrence of a pseudo color can be prevented and three primary color signals R 1 , G 1 , and B 1  (substantially) free from color mixing can be produced. 
     Note that, the video processor  204  is capable of producing three primary color signals R 1 , G 1 , and B 1  free from color mixing and therefore has the function and effect of effectively preventing, particularly in the narrow band imaging mode, the occurrence of a phenomenon in which color signals based on an optical image picked up under narrow band light of a particular color are made not easily discriminable due to color signals based on an optical image picked up under narrow band light of a different color. 
     The white balancing circuit  245  performs white balancing processing on the inputted three primary color signals R 1 , G 1 , and B 1  to produce and output three primary color signals R 2  G 2 , and B 2 . 
     A second matrix circuit  246  produces and outputs a luminance signal Y and color difference signals R-Y and B-Y on the basis of the three primary color signals R 2 ,  62 , and B 2  outputted from the white balancing circuit  245 . 
     In the normal imaging mode, in this case, the control circuit  215  sets matrix coefficients in the second matrix circuit  246  as coefficients only enabling generation of the luminance signal Y and the color difference signals R-Y and B-Y from the inputted three primary colors R 2 , G 2 , and B 2 . 
     In the narrow band imaging mode, the control circuit  215  sets matrix coefficients in the second matrix circuit  246  different from those in the normal imaging mode, as coefficients enabling generation of a luminance signal Ynbi having an increased proportion (weight) with respect to the B signal in particular and the color difference signals R-Y and B-Y from the inputted three primary colors R 2 , G 2 , and B 2 . 
     A conversion expression in the case of using matrices A and K of three rows and three columns in the cases shown above is as shown by expression (3) below. 
     
       
         
           
             
               
                 
                   
                     ( 
                     
                       
                         
                           Ynbi 
                         
                       
                       
                         
                           
                             R 
                             - 
                             Y 
                           
                         
                       
                       
                         
                           
                             B 
                             - 
                             Y 
                           
                         
                       
                     
                     ) 
                   
                   = 
                   
                     A 
                     * 
                     K 
                     * 
                     
                       ( 
                       
                         
                           
                             
                               R 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                           
                         
                         
                           
                             
                               G 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                           
                         
                         
                           
                             
                               B 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     Matrix K may be as shown by expression (4) below, having as its elements the values of the constant k 1 , the constant k 2  and the constant k 3  in expression (1) shown above, 
                   K   =     (         0         k   1         0           0       0         k   2             0         k   3         0         )             (   4   )               
or may be as shown by expression (5) below, having as its elements the values of the constant k 1 , the constant k 2 , the constant k 3  and the constant k 4  in expression (2) shown above.
 
     
       
         
           
             
               
                 
                   K 
                   = 
                   
                     ( 
                     
                       
                         
                           0 
                         
                         
                           
                             k 
                             1 
                           
                         
                         
                           0 
                         
                       
                       
                         
                           0 
                         
                         
                           0 
                         
                         
                           
                             k 
                             2 
                           
                         
                       
                       
                         
                           0 
                         
                         
                           
                             k 
                             3 
                           
                         
                         
                           
                             k 
                             4 
                           
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     Matrix A is a matrix for generating a Y color difference signal from RGB signals and uses, for example, known calculation coefficients such as those shown in expression (6) below. 
     
       
         
           
             
               
                 
                   A 
                   = 
                   
                     ( 
                     
                       
                         
                           0.299 
                         
                         
                           0.587 
                         
                         
                           0.114 
                         
                       
                       
                         
                           
                             - 
                             0.299 
                           
                         
                         
                           
                             - 
                             0.587 
                           
                         
                         
                           0.886 
                         
                       
                       
                         
                           0.701 
                         
                         
                           
                             - 
                             0.587 
                           
                         
                         
                           
                             - 
                             0.114 
                           
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     The luminance signal Ynbi outputted from the second matrix circuit  246  is inputted to the selector  239 . In the normal imaging mode, the selector  239  selects and outputs the luminance signal Yh under the control of the control circuit  215 . In the narrow band imaging mode, the selector  239  selects and outputs the luminance signal Ynbi under the control of the control circuit  215 . Note that, in  FIG. 7 , the luminance signal Yh or Ynbi selectively outputted from the selector  239  is shown as luminance signal Ysel. 
     The color difference signals R-Y and B-Y outputted from the second matrix circuit  246  are inputted to an enlargement/interpolation circuit  247  together with the luminance signal Ysel (luminance signal Yh or Ynbi) outputted via the selector  239 . 
     The luminance signal Ysel undergoes enlargement processing in the enlargement/interpolation circuit  247  and sharpness enhancement processing in an enhancement circuit  248  and is thereafter inputted to a third matrix circuit  249 . The color difference signals R-Y and B-Y having undergone enlargement processing in the enlargement/interpolation circuit  247  is also inputted to the third matrix circuit  249 . 
     The luminance signal Ysel and the color difference signals R-Y and B-Y undergo processing for conversion into three primary color signals R, G, and B in the third matrix circuit  249  and D/A conversion processing in a D/A conversion circuit  251  and is thereafter outputted from a video signal output end of the video processor  204  to the monitor  205 . 
     The control circuit  215  changes and sets the characteristic of the LPF  243 , the matrix coefficients in the first matrix circuit  242  and the matrix coefficients in the second matrix circuit  246  and selects the luminance signal Yh/Ynbi in the selector  239  according to change or selection of the imaging mode made by operating the mode change switch  214   a  or  214   b.    
     The control circuit  215  also controls the operation of the filter insertion/removal device  216  in the light source device  203  according to change of the imaging mode. Also, the control circuit  215  makes a gain setting in the white balancing circuit  245  at the time of white balancing. 
     Description will next be made of the operation of the endoscopic apparatus  201  according to the present embodiment. 
     An operator or the like first powers on the components of the endoscopic apparatus  201 , i.e., the endoscope  202 , the light source device  203 , the video processor  204  and the monitor  205  to activate the components. It is assumed that, in the activated state, the endoscope  202 , the light source device  203  and the video processor  204  are set in the normal imaging mode. 
     When detecting change of the imaging mode of the video processor  204  from the normal imaging mode to the narrow band imaging mode on the basis of the imaging mode change signal outputted from the mode change switch  214   a  or  214   b , the control circuit  215  performs control for inserting the narrow band filter  224  on the optical path of the lamp  220  on the filter insertion/removal device  216 . The control circuit  215  also performs control according to the narrow band imaging mode on the selector  239 , the first matrix circuit  242 , the second LPF  243 , the white balancing circuit  245  and the second matrix circuit  246  on the basis of the imaging mode change signal outputted from the mode change switch  214   a  or  214   b.    
     On the other hand, the light source device  203  supplies narrow band illumination light according to the transmission characteristics of the narrow band filter  224  to the light guide  213  under the control of the control circuit  215 . 
     The narrow band illumination light supplied from the light source device  203  is emitted to the outside through the light guide  213  and the illumination lens  227  to illuminate a surface of a living tissue such as an affected part in a body cavity. 
     An image of the subject illuminated with the narrow band illumination light is formed by the objective lens  228 , optically color-separated by the color separating filter  230 , picked-up by the CCD  229  and thereafter outputted as an image pickup signal to the video processor  204 . 
     The image pickup signal outputted to the video processor  204  has the signal components thereof extracted by the CDS circuit  232  and is converted into a digital signal by the A/D conversion circuit  234 , gain-controlled by the AGC circuit  238  and thereafter inputted to the Y/C separation circuit  237 . 
     The Y/C separation circuit  237  produces the luminance signal Yh and the color difference signals Cr and Cb on the basis of the inputted digital signal. The Y/C separation circuit  237  outputs the luminance signal Yh to the selector  239  and to the first LPF  241  and outputs the color difference signals Cr and Cb to the second LPF  243 . 
     The luminance signal Yh undergoes filtering processing in the first LPF  241  and is thereafter outputted as luminance signal Y 1  to the first matrix circuit  242 . The color difference signals Cr and Cb undergo filtering processing based on the (above-described) second passband characteristic of the second LPF  243 , synchronized by the synchronization circuit  244  and thereafter outputted to the first matrix circuit  242 . 
     The first matrix circuit  242  produces three primary color signals R 1 , G 1 , and B 1  according to the inputted luminance signal Y 1  and color difference signals Cr and Cb, and outputs the produced three primary color signals R 1 , G 1 , and B 1  to the white balancing circuit  245 . 
     The white balancing circuit  245  produces three primary color signals R 2 , G 2 , and B 2  by performing white balancing processing on the inputted three primary color signals R 1 , G 1 , and B 1 , and outputs the three primary color signals R 2 , G 2 , and B 2  to the second matrix circuit  246 . 
     The second matrix circuit  246  produces the luminance signal Ynbi and the color difference signals R-Y and B-Y by performing conversion processing based on expressions (3), (4), and (6) shown above on the inputted three primary color signals R 2 , G 2 , and B 2 . The second matrix circuit  246  outputs the luminance signal Ynbi to the selector  239  and outputs the color difference signals R-Y and B-Y to the enlargement/interpolation circuit  247 . 
     The selector  239  selects the luminance signal Ynbi under the control of the control circuit  215  and outputs the luminance signal Ynbi as luminance signal Ysel to the enlargement/interpolation circuit  247 . 
     The luminance signal Ysel undergoes enlargement processing in the enlargement/interpolation circuit  247  and sharpness enhancement processing in the enhancement circuit  248  and is thereafter inputted to the third matrix circuit  249 . The color difference signals R-Y and B-Y having undergone enlargement processing in the enlargement/interpolation circuit  247  is inputted to the third matrix circuit  249 . 
     The luminance signal Ysel and the color difference signals R-Y and B-Y undergo processing for conversion into three primary color signals R, G, and B in the third matrix circuit  249 , undergo the D/A conversion processing in the D/A conversion circuit  251  and are thereafter outputted from the video signal output end of the video processor  204  to the monitor  205 . 
     The above-described sequence of processing is performed in the video processor  204  to display an image of the subject in the narrow band imaging mode on the monitor  205 . For example, as an image of the subject in the narrow band imaging mode, images such as those in  FIG. 6 , i.e., an image in which images of capillaries  101  in the vicinity of a mucosal surface layer in the living body are emphasized, and an image of a residue  102 , as an image of a predetermined object different from living tissues, are displayed on the monitor  205 . Note that, the residue  102  may be any other predetermined object different from living tissues, e.g., bile or intestinal juice. 
     The images of capillaries  101  are displayed, for example, in brown or a color close to the brown as a result of the above-described matrix conversion processing performed in the video processor  204 . Also, the image of residue  102  is displayed, for example, in magenta or a color close to the magenta as a result of the above-described matrix conversion processing performed in the video processor  204 . That is, the second matrix circuit  246  performs processing in the above-described matrix conversion processing so that the luminance value of the red component and the luminance value of the blue component in the image of residue  102  are substantially equal to each other. 
     By the above-described working, the endoscopic apparatus  201  in the second embodiment can obtain in narrow band imaging an image in which capillaries in the vicinity of a mucosal surface layer in a living body are emphasized, and can also obtain an image in which an image of a residue has a color different from a red color substantially the same as that of blood. Thus, the endoscopic apparatus  201  in the second embodiment can reduce the burden on an operator or the like in a case where narrow band imaging is performed on a living body. 
     The second matrix circuit  246  may perform conversion processing based on expression (3), expression (5) and expression (6) shown above to obtain an effect similar to the above-described effect. 
     When matrix conversion processing based on expression (3), expression (5) and expression (6) shown above is performed, an image of residue  102  having substantially the same color as that of the image obtained when matrix conversion processing based on expression (3), expression (4) and expression (6) shown above is performed is displayed on the monitor  205 . Also, when matrix conversion processing based on expression (3), expression (5) and expression (6) shown above is performed, images of capillaries  101  having improved contrast in comparison with those obtained when matrix conversion processing based on expression (3), expression (4) and expression (6) is performed are displayed on the monitor  205 . 
     When matrix conversion processing based on expression (3), expression (4) and expression (6) shown above is performed, there is a possibility of an image of a local portion  103 , such as shown in  FIG. 6 , to be displayed on the monitor  205  as an image in a color extremely close to yellow due to a halation. On the other hand, when matrix conversion processing based on expression (3), expression (5) and expression (6) shown above is performed, an image of a local portion  103 , such as shown in  FIG. 6 , is displayed on the monitor  205  as an image in white or in a color close to white. 
     The above-described matrix conversion processing based on expression (3), expression (5) and expression (6) shown above is performed in the second matrix circuit  246  to display on the monitor  205  images of capillaries  101  having improved contrast in comparison with those obtained when matrix conversion processing based on expression (3), expression (4) and expression (6) is performed, an image of a residue  102  having a color different from a red color substantially the same as that of blood, and an image of a local portion  103  in white or in a color close to white. 
     Needless to say, the present invention is not limited to the above-described embodiments. Various changes and applications may be made without departing from the scope of the present invention.