Patent Publication Number: US-8531512-B2

Title: Endoscope apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of PCT/JP2005/015671 filed on Aug. 29, 2005 and claims the benefit of Japanese Applications No. 2004-250978 filed in Japan on Aug. 30, 2004, No. 2004-250979 filed in Japan on Aug. 30, 2004, No. 2004-252862 filed in Japan on Aug. 31, 2004, No. 2004-256140 filed in Japan on Sep. 2, 2004, No. 2004-256141 filed in Japan on Sep. 2, 2004, No. 2005-009477 filed in Japan on Jan. 17, 2005, and No. 2005-244083 filed in Japan on Aug. 25, 2005, the entire contents of each of which are incorporated herein by their reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an endoscope apparatus for capturing an image of living tissue and performing signal processing. 
     2. Description of the Related Art 
     An endoscope apparatus, which irradiates an illumination light and obtains an endoscopic image of the inside of a body cavity, has been widely utilized for some time now. This type of endoscope apparatus utilizes an electronic endoscope, which includes image-capturing means for introducing illumination light from a light-source apparatus using a light guide or the like inside a body cavity, and capturing an image of an object by the return light thereof, and by performing signal processing on the image-capturing signal from the image-capturing means using a video processor, displays an endoscopic image on an observation monitor for observation of a diseased part or other such observation site. 
     When performing ordinary observation of living tissue via an endoscope apparatus, a light-source apparatus emits white light in the visible light region, and, for example, irradiates surface-sequential light on an object via an RGB or other such rotating filter, and can produce a color image either by using a video processor to synchronize and perform image processing of the return light from the surface-sequential light, or by arranging a color chip on the front face of the image-capturing surface of the image-capturing means of the endoscope, capturing an image by separating the return light from the white light into its respective color components via the color chip, and using a video processor to perform image processing. 
     By contrast, since the absorption characteristics and scattering characteristics of light differ in accordance with the wavelength of irradiated light, for example, in Japanese Patent Laid-open No. 2002-95635, there is proposed a narrowband-light endoscope apparatus, which irradiates narrowband RGB surface-sequential light of discrete spectral characteristics of illumination light in the visible light region onto living tissue, and obtains tissue information of a desired depth of the living tissue. 
     SUMMARY OF THE INVENTION 
     An endoscope apparatus of the present invention includes an illumination light supplying unit for supplying illumination light; an endoscope having an image-capturing unit for irradiating the illumination light on an object, and capturing an image of the object by the return light; a two-band restricting unit for restricting the illumination light to a narrowband light of two band regions, and irradiating the narrowband light onto the object; and a signal processing unit for generating a first band region image data and a second band region image data in accordance with the narrowband light of the two band regions restricted and irradiated by the two-band restricting unit, and generating, from the first band region image data and the second band region image data, three-channel color image data for display on a displaying unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of an endoscope apparatus related to a first embodiment of the present invention; 
         FIG. 2  is a configuration diagram showing a configuration of the rotating filter of  FIG. 1 ; 
         FIG. 3  is a diagram showing spectral characteristics of a first filter group of the rotating filter of  FIG. 2 ; 
         FIG. 4  is a diagram showing spectral characteristics of a second filter group of the rotating filter of  FIG. 2 ; 
         FIG. 5  is a diagram showing the layered structure of a living tissue observed via the endoscope apparatus of  FIG. 1 ; 
         FIG. 6  is a diagram illustrating the access state in the direction of the layers of a living tissue of illumination light from the endoscope apparatus of  FIG. 1 ; 
         FIG. 7  is a first diagram showing the respective band images resulting from surface-sequential light permeating the first filter group of  FIG. 3 ; 
         FIG. 8  is a second diagram showing the respective band images resulting from surface-sequential light permeating the first filter group of  FIG. 3 ; 
         FIG. 9  is a third diagram showing the respective band images resulting from surface-sequential light permeating the first filter group of  FIG. 3 ; 
         FIG. 10  is a first diagram showing the respective band images resulting from surface-sequential light permeating the second filter group of  FIG. 4 ; 
         FIG. 11  is a second diagram showing the respective band images resulting from surface-sequential light permeating the second filter group of  FIG. 4 ; 
         FIG. 12  is a first diagram illustrating a manufacturing method of the second filter group of  FIG. 4 ; 
         FIG. 13  is a second diagram illustrating a manufacturing method of the second filter group of  FIG. 4 ; 
         FIG. 14  is a third diagram illustrating a manufacturing method of the second filter group of  FIG. 4 ; 
         FIG. 15  is a fourth diagram illustrating a manufacturing method of the second filter group of  FIG. 4 ; 
         FIG. 16  is a fifth diagram illustrating a manufacturing method of the second filter group of  FIG. 4 ; 
         FIG. 17  is a sixth diagram illustrating a manufacturing method of the second filter group of  FIG. 4 ; 
         FIG. 18  is a seventh diagram illustrating a manufacturing method of the second filter group of  FIG. 4 ; 
         FIG. 19  is a block diagram showing a configuration of a variation of the endoscope apparatus of  FIG. 1 ; 
         FIG. 20  is a diagram showing the spectral transmission characteristics of the narrowband interference filter of  FIG. 19 ; 
         FIG. 21  is a diagram showing the spectral transmission characteristics of a first interference membrane filter for realizing the narrowband interference filter of  FIG. 19 ; 
         FIG. 22  is a diagram showing the spectral transmission characteristics of a second interference membrane filter for realizing the narrowband interference filter of  FIG. 19 ; 
         FIG. 23  is a diagram showing the spectral transmission characteristics of a third interference membrane filter for realizing the narrowband interference filter of  FIG. 19 ; 
         FIG. 24  is a diagram showing the spectral transmission characteristics of a variation of the narrowband interference filter of  FIG. 20 ; 
         FIG. 25  is a configuration diagram showing a configuration of a first variation of the rotating filter of  FIG. 1 ; 
         FIG. 26  is a configuration diagram showing a configuration of a second variation of the rotating filter of  FIG. 1 ; 
         FIG. 27  is a diagram showing a configuration of an endoscope apparatus when the rotating filter of  FIG. 26  is used; 
         FIG. 28  is a block diagram showing a configuration of an endoscope apparatus according to a second embodiment of the present invention; 
         FIG. 29  is a diagram showing a configuration of a filter array of color separating filters provided in a solid-state image-capturing device; 
         FIG. 30  is a characteristic diagram showing the spectral characteristics of a narrowband filter; 
         FIG. 31  is a diagram showing an example of a configuration of a modulated-light signal generation circuit; 
         FIG. 32  is a flowchart for explaining the operation of the second embodiment; 
         FIG. 33  is a diagram showing a configuration of peripheral portions of the modulated-light signal generation circuit of a variation of the second embodiment; 
         FIG. 34  is a simplified block diagram of a conventional surface-sequential-type endoscope apparatus; 
         FIG. 35  is a simplified block diagram of a conventional synchronous-type endoscope apparatus; 
         FIG. 36  is a block diagram showing a configuration of an endoscope apparatus according to a third embodiment of the present invention; 
         FIG. 37  is a diagram showing a configuration and transmission characteristics of a rotating filter; 
         FIG. 38  is a circuit diagram showing a configuration of the modulated-light signal generation circuit; 
         FIG. 39  is a block diagram showing a configuration of the video processor of a variation of the third embodiment; 
         FIG. 40  is a block diagram showing a configuration of an endoscope apparatus according to a fourth embodiment of the present invention; 
         FIG. 41  is a diagram showing a configuration of a filter array of color separating filters provided in a solid-state image-capturing device; 
         FIG. 42  is a characteristics diagram showing an example of the spectral characteristics of a narrowband filter; 
         FIG. 43  is a flowchart for explaining the operation of the fourth embodiment; 
         FIG. 44  is a diagram showing the signal bands for a luminance signal and color difference signals; 
         FIG. 45  is a diagram showing coefficients of a second matrix circuit set in a first variation of the fourth embodiment that takes into account the characteristics of  FIG. 44 ; 
         FIG. 46  is a characteristic diagram showing the spectral characteristics of a narrowband filter in a second variation of the fourth embodiment; 
         FIG. 47  is a diagram showing coefficients of a second matrix circuit set in the second variation of  FIG. 46 ; 
         FIG. 48  is a block diagram showing a configuration of a video signal processing apparatus of a conventional example; 
         FIG. 49  is a block diagram showing a configuration of an endoscope apparatus according to a fifth embodiment of the present invention; 
         FIG. 50  is an external view showing the external configuration of an endoscope apparatus related to the first embodiment of the present invention; 
         FIG. 51  is a diagram showing the front panel of the light-source apparatus of  FIG. 50 ; 
         FIG. 52  is a diagram showing the front panel of the video processor of  FIG. 50 ; 
         FIG. 53  is block diagram showing a configuration of the endoscope apparatus of  FIG. 50 ; 
         FIG. 54  is a block diagram showing a configuration of the rotating filter of  FIG. 53 ; 
         FIG. 55  is a diagram showing the spectral characteristics of a first filter group of the rotating filter of  FIG. 54 ; 
         FIG. 56  is a diagram showing the spectral characteristics of a second filter group of the rotating filter of  FIG. 54 ; 
         FIG. 57  is a diagram showing the layered structure of a living tissue observed via the endoscope apparatus of  FIG. 53 ; 
         FIG. 58  is a diagram illustrating the access state in the direction of the layers of a living tissue of illumination light from the endoscope apparatus of  FIG. 53 ; 
         FIG. 59  is a first diagram showing the respective band images resulting from the surface-sequential light permeating the first filter group of  FIG. 55 ; 
         FIG. 60  is a second diagram showing the respective band images resulting from the surface-sequential light permeating the first filter group of  FIG. 55 ; 
         FIG. 61  is a third diagram showing the respective band images resulting from the surface-sequential light permeating the first filter group of  FIG. 55 ; 
         FIG. 62  is a first diagram showing the respective band images resulting from the surface-sequential light permeating the second filter group of  FIG. 56 ; 
         FIG. 63  is a second diagram showing the respective band images resulting from the surface-sequential light permeating the second filter group of  FIG. 56 ; 
         FIG. 64  is a block diagram showing a configuration of the white balance circuit of  FIG. 53 ; 
         FIG. 65  is an external view showing the external configuration of a first variation of the endoscope apparatus of  FIG. 50 ; 
         FIG. 66  is an external view showing the external configuration of a second variation of the endoscope apparatus of  FIG. 50 ; 
         FIG. 67  is a block diagram showing a configuration of a synchronous-type endoscope apparatus, which is a variation of the endoscope apparatus of  FIG. 53 ; 
         FIG. 68  is a block diagram showing a configuration of the white balance circuit of  FIG. 67 ; 
         FIG. 69  is a block diagram showing a configuration of a white balance circuit related to a seventh embodiment of the present invention; 
         FIG. 70  is a block diagram showing a configuration of an endoscope apparatus related to an eighth embodiment of the present invention; 
         FIG. 71  is a block diagram showing a configuration of the rotating filter of  FIG. 70 ; 
         FIG. 72  is a diagram showing the spectral characteristics of a first filter group of the rotating filter of  FIG. 71 ; 
         FIG. 73  is a diagram showing the spectral characteristics of a second filter group of the rotating filter of  FIG. 71 ; 
         FIG. 74  is a diagram showing the layered structure of a living tissue observed via the endoscope apparatus of  FIG. 70 ; 
         FIG. 75  is a diagram illustrating the access state in the direction of the layers of a living tissue of the illumination light from the endoscope apparatus of  FIG. 70 ; 
         FIG. 76  is a first diagram showing the respective band images resulting from the surface-sequential light permeating the first filter group of  FIG. 72 ; 
         FIG. 77  is a second diagram showing the respective band images resulting from the surface-sequential light permeating the first filter group of  FIG. 72 ; 
         FIG. 78  is a third diagram showing the respective band images resulting from the surface-sequential light permeating the first filter group of  FIG. 72 ; 
         FIG. 79  is a first diagram showing the respective band images resulting from the surface-sequential light permeating the second filter group of  FIG. 73 ; 
         FIG. 80  is a second diagram showing the respective band images resulting from the surface-sequential light permeating the second filter group of  FIG. 73 ; 
         FIG. 81  is a third diagram showing the respective band images resulting from the surface-sequential light permeating the second filter group of  FIG. 73 ; 
         FIG. 82  is a block diagram showing a configuration of the white balance circuit of  FIG. 70 ; 
         FIG. 83  is a block diagram showing a configuration of a variation of the white balance circuit of  FIG. 82 ; 
         FIG. 84  is a block diagram showing a configuration of a first variation of the endoscope apparatus of  FIG. 70 ; 
         FIG. 85  is a block diagram showing a configuration of the white balance circuit of  FIG. 84 ; 
         FIG. 86  is a block diagram showing a configuration of a second variation of the endoscope apparatus of  FIG. 70 ; 
         FIG. 87  is a block diagram showing a configuration of the white balance circuit of  FIG. 86 ; and 
         FIG. 88  is a block diagram showing a configuration of a variation of the white balance circuit of  FIG. 86 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     The embodiments of the present invention will be explained below by referring to the figures. 
     First Embodiment 
       FIGS. 1 through 27  are related to a first embodiment of the present invention.  FIG. 1  is a block diagram showing a configuration of an endoscope apparatus;  FIG. 2  is a configuration diagram showing a configuration of the rotating filter of  FIG. 1 ;  FIG. 3  is a diagram showing the spectral characteristics of a first filter group of the rotating filter of  FIG. 2 ;  FIG. 4  is a diagram showing the spectral characteristics of a second filter group of the rotating filter of  FIG. 2 ;  FIG. 5  is a diagram showing the layered structure of a living tissue observed via the endoscope apparatus of  FIG. 1 ;  FIG. 6  is a diagram illustrating the access state in the direction of the layers of a living tissue of illumination light from the endoscope apparatus of  FIG. 1 ;  FIG. 7  is a first diagram showing the respective band images resulting from surface-sequential light permeating the first filter group of  FIG. 3 ;  FIG. 8  is a second diagram showing the respective band images resulting from surface-sequential light permeating the first filter group of  FIG. 3 ;  FIG. 9  is a third diagram showing the respective band images resulting from surface-sequential light permeating the first filter group of  FIG. 3 ;  FIG. 10  is a first diagram showing the respective band images resulting from surface-sequential light permeating the second filter group of  FIG. 4 ;  FIG. 11  is a second diagram showing the respective band images resulting from surface-sequential light permeating the second filter group of  FIG. 4 ;  FIG. 12  is a first diagram illustrating a manufacturing method of the second filter group of  FIG. 4 ;  FIG. 13  is a second diagram illustrating a manufacturing method of the second filter group of  FIG. 4 ;  FIG. 14  is a third diagram illustrating a manufacturing method of the second filter group of  FIG. 4 ;  FIG. 15  is a fourth diagram illustrating a manufacturing method of the second filter group of  FIG. 4 ;  FIG. 16  is a fifth diagram illustrating a manufacturing method of the second filter group of  FIG. 4 ;  FIG. 17  is a sixth diagram illustrating a manufacturing method of the second filter group of  FIG. 4 ;  FIG. 18  is a seventh diagram illustrating a manufacturing method of the second filter group of  FIG. 4 ;  FIG. 19  is a block diagram showing a configuration of a variation of the endoscope apparatus of  FIG. 1 ;  FIG. 20  is a diagram showing the spectral transmission characteristics of the narrowband interference filter of  FIG. 19 ;  FIG. 21  is a diagram showing the spectral transmission characteristics of a first interference membrane filter for realizing the narrowband interference filter of  FIG. 19 ;  FIG. 22  is a diagram showing the spectral transmission characteristics of a second interference membrane filter for realizing the narrowband interference filter of  FIG. 19 ;  FIG. 23  is a diagram showing the spectral transmission characteristics of a third interference membrane filter for realizing the narrowband interference filter of  FIG. 19 ;  FIG. 24  is a diagram showing the spectral transmission characteristics of a variation of the narrowband interference filter of  FIG. 20 ;  FIG. 25  is a configuration diagram showing a configuration of a first variation of the rotating filter of  FIG. 1 ;  FIG. 26  is a configuration diagram showing a configuration of a second variation of the rotating filter of  FIG. 1 ; and  FIG. 27  is a diagram showing a configuration of an endoscope apparatus when the rotating filter of  FIG. 26  is used. 
     As shown in  FIG. 1 , an endoscope apparatus  1  of the present embodiment includes an electronic endoscope  3 , which is inserted into a body cavity, and has a CCD  2  as image-capturing means for capturing an image of a tissue inside the body cavity; a light-source apparatus  4  for supplying an illumination light to the electronic endoscope  3 ; and a video processor  7 , which performs signal processing of an image-capturing signal from the CCD  2  of the electronic endoscope  3 , and displays the endoscopic image on an observation monitor  5 , and encodes the endoscopic image and outputs the same to an image filing apparatus  6  as a compressed image. 
     The light-source apparatus  4  includes a xenon lamp  11  for emitting an illumination light; a heat cutting filter  12  for blocking the heat of a white light; a diaphragm device  13  for controlling the quantity of light of a white light via the heat cutting filter  12 ; a rotating filter  14  for making the illumination light a surface-sequential light; a condensing lens  16  for condensing the surface-sequential light via the rotating filter  14  on the incident surface of a light guide  15  arranged inside the electronic endoscope  3 ; and a control circuit  17  for controlling the rotation of the rotating filter  14 . 
     The rotating filter  14 , as shown in  FIG. 2 , is constituted in a disk shape, and has a dual structure centered around an axis of rotation, an R 1  filter section  14   r   1 , a G 1  filter section  14   g   1 , and a B 1  filter section  14   b   1 , which constitute a first filter group for outputting surface-sequential light of overlapping spectral characteristics, which, as shown in  FIG. 3 , is well suited to color reproduction, are arranged in the outer radial part, and a G 2  filter section  14   g   2 , a B 2  filter section  14   b   2 , and a shading filter section  14 Cut, which constitute a second filter group for outputting narrowband surface-sequential light of two bands of discrete spectral characteristics, capable, as shown in  FIG. 4 , of extracting the desired layer tissue information, are arranged in the inner radial part. 
     Furthermore, it is supposed, for example, that the wavelength region λ 11  through λ 12  of the B 2  filter section  14   b   2  is between 405 and 425 nm, and the wavelength region λ 21  through λ 22  of the G 2  filter section  14   g   2  is between 530 and 550 nm. 
     Furthermore, the wavelength region λ 11  through λ 12  may be between 400 and 440 nm, and the wavelength region λ 21  through λ 22  may be between 530 and 550 nm. 
     Then, as shown in  FIG. 1 , a control circuit  17  drives and controls a rotating filter motor  18 , thereby rotating the rotating filter  14 , and a mode switching motor  19  moves the rotating filter  14  radially (moves the rotating filter  14  perpendicular to the optical path, and selectively moves the first filter group and second filter group of the rotating filter  14  into the optical path) in accordance with a control signal from a mode switching circuit  42  inside the video processor  7 , which will be explained hereinbelow. 
     Furthermore, power is supplied to the xenon lamp  11 , diaphragm device  13 , rotating filter motor  18 , and mode switching motor  19  from a power unit  10 . 
     The video processor  7  includes a CCD drive circuit  20  for driving the CCD  2 ; an amplifier  22  for amplifying an image-capturing signal, which is an image of a body cavity tissue captured by the CCD  2  through an objective optical system  21 ; a processing circuit  23 , which performs correlated double sampling (CDS) and noise removal for an image-capturing signal through the amplifier  22 ; an A/D converter  24  for converting an image-capturing signal that has passed through the processing circuit  23  to digital signal image data; a white balance circuit (W.B.)  25  for performing white balance processing on the image data from the A/D converter  24 ; a selector  26  and synchronization memories  27 ,  28 ,  29  for synchronizing surface-sequential light using the rotating filter  14 ; an image processing circuit  30  for reading out the respective image data of the surface-sequential light stored in the synchronization memories  27 ,  28 ,  29 , and performing gamma correction processing, contour highlight processing, and color processing; D/A circuits  31 ,  32 ,  33  for converting image data from the image processing circuit  30  to analog signals; an encoding circuit  34  for encoding image data from the image processing circuit  30 ; and a timing generator (T.G.)  35  for inputting from the control circuit  17  of the light-source apparatus  4  a synchronization signal synchronized to the rotation of the rotating filter  14 , and outputting various timing signals to the above-described respective circuits. 
     Further, a mode-switching switch  41  is provided in the electronic endoscope  2 , and the output of the mode-switching switch  41  is outputted to the mode switching circuit  42  inside the video processor  7 . The mode switching circuit  42  of the video processor  7  outputs a control signal to light modulation circuit  43 , a light modulation control parameter switching circuit  44 , and the mode switching motor  19  of the light-source apparatus  4 . The light modulation control parameter switching circuit  44  outputs a light modulation control parameter corresponding to the first filter group and the second filter group of the rotating filter  14  to the light modulation circuit  43 , and the light modulation circuit  43  controls the diaphragm device  13  of the light-source apparatus  4  based on a control signal from the mode switching circuit  42  and a light modulation control parameter from the light modulation control parameter switching circuit  44  so as to control optimum brightness. 
     Next, the operation of the endoscope apparatus of the present embodiment, which is constituted, will be explained. 
     As shown in  FIG. 5 , in most cases, for example, body cavity tissue  51  has an absorbent distributed structure of blood vessels and the like that differ in the depth direction. In the vicinity of the superficial portion of the mucous membrane mainly capillary vessels  52  are distributed in large numbers, and in the intermediate layer, which is deeper than this layer, blood vessels  53  that are larger than capillary vessels are distributed in addition to capillary vessels, and in a yet deeper layer, even larger blood vessels  54  are distributed. 
     Meanwhile, the invasion depth in the depth direction of light relative to a body cavity tissue  51  is dependent on the wavelength of the light, and when illumination light including the visible region is a short wavelength like that of blue (B), as shown in  FIG. 6 , the light only penetrates as far as the superficial layer as a result of the absorption characteristics and scattering characteristics of the living tissue, is subjected to absorption and scattering in that depth range, and the light that exits from the surface is observed. Further, in the case of green (G) light, which has a longer wavelength than blue (B) light, the light penetrates deeper than the range to which the blue (B) light penetrated, is subjected to absorption and scattering in that range, and the light that exists from the surface is observed. And red (R) light, which has a longer wavelength than green (G) light, reaches an even deeper range. 
     In ordinary observation, the mode switching circuit inside the video processor  7  controls the mode switching motor  19  via a control signal such that the R 1  filter section  14   r   1 , G 1  filter section  14   g   1 , and B 1  filter section  14   b   1 , which are the first filter group of the rotating filter  14 , are located in the optical path of the illumination light. 
     Since the respective wavelength regions of the R 1  filter section  14   r   1 , G 1  filter section  14   g   1 , and B 1  filter section  14   b   1  overlap one another as shown in  FIG. 3  during ordinary observation of the body cavity tissue  51 , (1) a band image including shallow layer and intermediate layer tissue information, which includes plenty of tissue information of the shallow layer as shown in  FIG. 7 , is captured in an image-capturing signal, which is an image captured by the CCD  2  via the B 1  filter section  14   b   1 ; (2) also, a band image including shallow layer and intermediate layer tissue information, which includes plenty of tissue information of the intermediate layer as shown in  FIG. 8 , is captured in an image-capturing signal, which is an image captured by the CCD  2  via the G 1  filter section  14   g   1 ; and (3) in addition, a band image including intermediate layer and deep layer tissue information, which includes plenty of tissue information of the deep layer as shown in  FIG. 9 , is captured in an image-capturing signal, which is an image captured by the CCD  2  via the R 1  filter section  14   r   1 . 
     Then, an endoscopic image of a desired or natural color reproduction can be obtained as the endoscopic image by the video processor  7  synchronizing the RGB image-capturing signals and performing signal processing. 
     By contrast, if the mode-switching switch  41  of the electronic endoscope  3  is pressed, the signal is inputted to the mode switching circuit  42  of the video processor  7 . By outputting a control signal to the mode switching motor  19  of the light-source apparatus  4 , the mode switching circuit  42  drives the rotating filter  14  relative to the optical path so as to move the first filter group of the rotating filter  14 , which was in the optical path at ordinary observation, and position the second filter group in the optical path. 
     Because the G 2  filter section  14   g   2 , B 2  filter section  14   b   2 , and shading filter section  14 Cut change the illumination light to two-band narrowband surface-sequential light of discrete spectral characteristics, and their respective wavelength regions do not overlap as shown in  FIG. 4  when body cavity tissue  51  is being observed under narrowband light using the second filter group, (4) a band image including tissue information of the shallow layer as shown in  FIG. 10  is captured in the image-capturing signal, which is an image captured by the CCD  2  via the B 2  filter section  14   b   2 ; and (5) a band image including tissue information of the intermediate layer as shown in  FIG. 11  is also captured in the image-capturing signal, which is an image captured by the CCD  2  via the G 2  filter section  14   g   2 . 
     As is clear from  FIGS. 3 and 4 , since the quantity of light transmitted by the second filter group decreases relative to the quantity of light transmitted by the first filter group due to the narrowing of the band thereof, the light modulation control parameter switching circuit  44  outputs to the light modulation circuit  43  a light modulation control parameter corresponding to the first filter group and second filter group of the rotating filter  14 , and the light modulation circuit  43  controls the diaphragm device  13 , thereby obtaining sufficiently bright image data even when observation is being carried out under narrowband light. 
     Further, the image processing circuit  30 , when colorizing an image at narrowband-light observation, generates an RGB three-channel color image as R-channel←G-narrowband image data, G-channel←B-narrowband image data, and B-channel←B-narrowband image data. 
     That is, the image processing circuit  30  generates RGB three-channel color images (R′, G′, B′) relative to G-narrowband image data (G) and B-narrowband image data (B). 
     
       
         
           
             
               
                 
                   
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     For example, it is supposed that h11=1, h12=0, h21=0, h22=1.2, h31=0, and h32=0.8. 
     Since a conventional three-band narrowband surface-sequential light like that shown in  FIG. 12  is obtained, the vapor deposition of an interference membrane filter having spectral transmittance characteristics like those shown in  FIGS. 13 and 14  for B narrowband light, the vapor deposition of an interference membrane filter having spectral transmittance characteristics like those shown in  FIGS. 15 and 16  for G narrowband light, and the vapor deposition of an interference membrane filter having spectral transmittance characteristics like those shown in  FIGS. 17 and 18  for R narrowband light become necessary, but in the present embodiment, the B 2  filter section  14   b   2  is manufactured by the vapor deposition of an interference membrane filter having spectral transmittance characteristics like those shown in  FIGS. 13 and 14 , and the G 2  filter section  14   g   2  is manufactured by the vapor deposition of an interference membrane filter having spectral transmittance characteristics like those shown in  FIGS. 15 and 16 . 
     When an optical filter is manufactured like this, ordinarily the problem is that in most cases this is done by vapor deposition of a multi-layered interference membrane filter, and, in the manufacturing method, to make the spectral transmittance characteristics narrowband, a number of membranes must be deposited, thus raising costs and increasing the thickness of the filter. However, in the present embodiment, tissue information of a desired depth in the vicinity of the superficial portion of the mucous membrane can be obtained by vapor depositioning the smallest multi-layered interference membrane filter possible, and, for example, can be used in the identification and diagnosis of early-stage cancer and other such diseases that disturb the cellular arrangement in the vicinity of the superficial portion of the mucous membrane. 
     Furthermore, for the endoscope apparatus  1  of the above-described embodiment, an example of a surface-sequential-type endoscope apparatus, in which a light-source apparatus  4  supplies surface-sequential light, and a video processor  7  synchronizes surface-sequential image data to create an image was used in the explanation, but the first embodiment is not limited to this, and a synchronous-type endoscope apparatus is also applicable. 
     That is, as shown in  FIG. 19 , a synchronous-type endoscope apparatus  1   a , including a light-source apparatus  4   a  for supplying white light; an electronic endoscope  3   a , which comprises a color chip  100  on the front face of the image-capturing surface of the CCD  2 ; and a video processor  7   a  for carrying out signal processing of an image-capturing signal from the electronic endoscope  3   a , can also apply the present embodiment. 
     In the light-source apparatus  4   a , the quantity of light of the white light from the xenon lamp  11  by way of the heat cutting filter  12  is controlled by the diaphragm device  13 , and outputted to the incident surface of the light guide  15  disposed inside the electronic endoscope  3   a . A narrowband interference filter  14   a , which converts the white light to two bands of narrowband light A 1 , A 2  of discrete spectral characteristics as shown in  FIG. 20  is removably provided in the optical path of the white light. 
     Furthermore, the narrowband light A 1  and narrowband light A 2  of the narrowband interference filter  14   a  can be realized by the vapor depositioning of a plurality of interference membrane filters having spectral transmittance characteristics like those shown in  FIGS. 21 through 23 . Here, it is supposed that the wavelength region of narrowband light A 1  and the wavelength region of narrowband light A 2  include the following respective combinations: 
     Narrowband light A 1 =405 through 425 nm, narrowband light A 2 =530 through 550 nm 
     Narrowband light A 1 =405 through 425 nm, narrowband light A 2 =490 through 510 nm 
     Narrowband light A 1 =405 through 425 nm, narrowband light A 2 =440 through 460 nm 
     Narrowband light A 1 =440 through 460 nm, narrowband light A 2 =530 through 550 nm 
     However, the near ultraviolet region and near infrared region can also be included. 
     In the electronic endoscope  3   a , an image of a body cavity tissue  51  is captured by the CCD  2  through a color chip  100 . 
     In the video processor  7   a , image data from the A/D converter  24  is separated into a luminance signal Y and color difference signals Cr, Cb by a Y/C separation circuit  101 , converted to RGB signals by the RGB matrix circuit  102 , and outputted to the white balance circuit  25 . The rest of the configuration and operations are the same as the endoscope apparatus of  FIG. 1 . 
     Further, since the light of the R narrowband component is not irradiated onto the body cavity tissue  51 , tissue information resulting from R narrowband light is not included in the data obtained at narrowband-light observation, having the effect of enabling the acquisition of tissue information of a desired depth in the vicinity of a superficial portion of the mucous membrane without separating the image information using the light of the R narrowband component, and facilitating data processing. 
     Furthermore, as in the spectral transmittance characteristics of the B 2  filter section  14   b   2  and G 2  filter section  14   g   2  in the second filter group of the rotating filter  14  shown in  FIG. 24 , the spectral product of the G narrowband light can be smaller than the spectral product of the B narrowband light. The same holds true for narrowband light A 1  (equivalent to B narrowband light) and narrowband light A 2  (equivalent to G narrowband light) of the narrowband interference filter  14   a.    
     Alternatively, the spectral product SG of the G narrowband light is made smaller than the spectral product SB of the B narrowband light in the incident light to the CCD  2 . For example, it can be 1.10≦SG/SB≦0.35. 
     SG=∫ G S(λ)d λ 
     SB=∫ B S(λ)d λ 
     S(λ)=Lamp(λ)×LIRCut(λ)×NBIFilter(λ)×LG(λ)×IRCut(λ)×YagCut(λ) 
     Lamp(λ): spectral characteristics of the lamp 
     LIRCut(λ): spectral characteristics of the heat cutting filter inside the light-source apparatus 
     NBIFilter(λ): spectral characteristics of the narrowband interference filter (NBI filter) 
     LG(λ): spectral characteristics of the light guide 
     IRCut(λ): spectral characteristics of the infrared light cutting filter inside the endoscope apparatus 
     YagCut(λ): spectral characteristics of the laser light cutting filter inside the endoscope apparatus 
     Here ∫ G , ∫ B  indicate integration operations in the wavelength regions of the respective G narrowband light and B narrowband light. 
     In the past, the design of the transmittance of the narrowband interference filter (NBI filter) was done such that the white balance correction value became practically equivalent in RGB in order to suppress the noise in the R and B signals when photographing a white cap (standard white plate). 
     However, since absorbance by the Hb (hemoglobin) when observing a living mucous membrane is higher with B narrowband light than with G narrowband light, the B signal becomes relatively dark. In order to enhance the visibility of the mucous membrane data of the NBI using color conversion processing, it is necessary to make the brightness of the G and B signals practically equal, but the problem is that the noise of the B signal becomes conspicuous due to the need to increase the gain of the B signal. Furthermore, if transmittance adjustment is not proper in the complementary color filter CCD, the saturation points of Y/Cr/Cb differ for each signal, and color reproducibility deteriorates in RGB signals converted from YCrCb signals via a linear operation. 
     Accordingly, making the spectral product of G narrowband light smaller than the spectral product of B narrowband light enables the realization of good image quality by NBI. 
     That is, lowering the transmittance of the G narrowband than that of the B narrowband makes it possible to reduce the difference in the G and B signal outputs when observing a living mucous membrane, and since the gain of the B signal can be reduced as a result of this, noise can be suppressed. 
     Further, since the saturation point differences of Y/Cr/Cb can be lessened when observing a living mucous membrane, it becomes possible to widen the range within which brightness-related signal output linearly changes in the post-conversion signals, with the result that the range of color reproducibility also broadens. 
     Furthermore, the second filter group of the rotating filter  14  in  FIG. 1  includes a G 2  filter section  14   g   2 , a B 2  filter section  14   b   2 , and a shading filter section  14 Cut (refer to  FIG. 2 ), but as shown in  FIG. 25 , a B 2  filter section  14   b   2  can also be arranged in the shading filter section  14 Cut part, such that the second filter group constitutes a B 2  filter section  14   b   2 , a G 2  filter section  14   g   2 , and a B 2  filter section  14   b   2 . By constituting the second filter group like this, image-capturing by the CCD  2  via the B 2  filter section  14   b   2  is implemented twice in a single filter period and the image-capturing signal is processed, making it possible to improve the brightness of the narrowband B image, for example, by performing B addition processing, and to enhance the signal-to-noise ratio (SN) by averaging. 
     Further, the light-source apparatus  4  may be constituted by constituting the dual-structure rotating filter  14  in  FIG. 1  as a rotating filter  140  with only a first filter group, which comprises an R 1  filter section  14   r   1 , G 1  filter section  14   g   1 , and B 1  filter section  14   b   1  of the single structure shown in  FIG. 26 , and, as shown in  FIG. 27 , removably arranging the narrowband interference filter  14   a  shown in  FIG. 19  in the optical axis at the first stage of the incidence optical axis of the rotating filter  140 . In this case, ordinary surface-sequential light observation and narrowband surface-sequential light observation become possible using the video processor  7  of the configuration shown in  FIG. 1  without having to provide a color chip  100  on the front face of the CCD  2 . 
     Second Embodiment 
       FIGS. 28 through 35  are related to a second embodiment of the present invention.  FIG. 28  shows a configuration of an endoscope apparatus according to a second embodiment of the present invention;  FIG. 29  shows a configuration of a filter array of color separating filters provided in a solid-state image-capturing device;  FIG. 30  shows the spectral characteristics of a narrowband filter;  FIG. 31  shows a configuration of modulated-light signal generation circuit;  FIG. 32  shows a flowchart for explaining the operation of the present embodiment;  FIG. 33  shows a configuration of peripheral portions of the modulated-light signal generation circuit in a variation of the second embodiment;  FIG. 34  shows a configuration of a simplified block diagram of a conventional surface-sequential-type endoscope apparatus; and  FIG. 35  shows a simplified block diagram of a conventional synchronous-type endoscope apparatus. 
     The electronic endoscope including image-capturing means has come into widespread use in recent years in a variety of endoscopic examinations. 
     Further, an endoscope apparatus, which obtains a narrowband-light observation image using a narrowband illumination light has been commercialized recently. 
       FIG. 34  shows a simplified configuration of a conventional endoscope apparatus  1070 , which employs a surface-sequential system, and can obtain an ordinary-light observation image and a narrowband-light observation image. 
     A light-source apparatus  1071  illuminates an object by emitting broadband R, G and B surface-sequential illumination light at ordinary-light observation, and emitting narrowband R, G and B surface-sequential illumination light at narrowband-light observation. 
     The illuminated object is surface-sequentially captured as an image by a CCD  1072 . The CCD  1072  does not have a color filter for color separation provided on the image-capturing surface of the CCD, that is, it is a monochrome CCD. A surface-sequential image-capturing signal, which has undergone photoelectric transfer by the CCD  1072 , is inputted to a CDS circuit  1074  of a video processing circuit  1073 , and after a signal component has been extracted, is inputted to an A/D conversion circuit  1075 , and, in addition, is inputted to a luminance detection circuit  1076 . 
     A surface-sequential analog signal, which is inputted to the A/D conversion circuit  1075 , is converted to a digital signal, and thereafter inputted to a synchronization circuit  1077  and converted to a synchronized RGB signal. The RGB signal outputted from the synchronization circuit  1077  is subjected to enlargement processing in an enlargement circuit  1078 , after which it is inputted to a highlighting circuit  1079 , and subsequent to contour highlighting, is outputted from an output terminal to a monitor not shown in the figure, and an endoscopic image of either an ordinary-light observation mode or a narrowband-light observation mode is displayed in color. 
     Further, the luminance detection circuit  1076  integrates inputted surface-sequential R, G and B signals, generates a light modulation reference signal, and outputs a signal of the difference with the reference brightness value to the light-source apparatus  1071  as a modulated-light signal. Then, the light-source apparatus  1071  adjusts the quantity of illumination light in accordance with the modulated-light signal. 
     In the prior art, it is possible to properly modulate light using a light modulation reference signal generated at ordinary-light observation, but since the illumination light constitutes a narrowband at narrowband-light observation, the quantity of illumination light is reduced, and appropriate light modulation cannot be carried out with the same light modulation reference signal generating means as that used at ordinary-light observation. 
     Further, at ordinary-light observation, the brightness of the image can be regulated at a luminance level, which comprises all the respective color component signals, but the drawback is that, since specified color signals can constitute important image data at narrowband-light observation, generating a light modulation reference signal the same as at ordinary-light observation does not enable proper light modulation across a broad range of light quantities. 
     That is, light modulation can be carried out in accordance with the average value of the respective signals at ordinary-light observation, but the disadvantage is that, since the image data of specified color components is important at narrowband-light observation, it is not possible to carry out proper light modulation simply using the average value of the respective signals. 
     Furthermore, a prior art endoscope apparatus, which employs a surface-sequential system, and is capable of obtaining an ordinary-light observation image and a narrowband-light observation image, for example, is disclosed in Japanese Patent Laid-open No. 2002-95635. In the official gazette, a light modulation control parameter is changed in a common light modulation circuit at ordinary-light observation and at narrowband-light observation. 
     According to the prior art of the official gazette, light modulation can be improved more than in the case of the circuit configuration of  FIG. 34 , but the disadvantage is that it is difficult to properly modulate light at narrowband-light observation even when the light modulation control parameter is changed due to the fact that a common light modulation circuit is being employed. 
     Meanwhile,  FIG. 35  shows a simplified configuration of a conventional synchronous-type endoscope apparatus  1080  that performs an ordinary-light observation and a narrowband-light observation using an endoscope equipped with image-capturing means including an optical filter. 
     A light-source apparatus  1081  generates an illumination light of white light at ordinary-light observation, and generates an illumination light of R, G and B narrowband light at narrowband-light observation, and illuminates an object. 
     The illuminated object is captured as an image by a CCD  1083  to which a color filter  1082  is provided on the image-capturing surface. An image-capturing signal, which has undergone photoelectric transfer by the CCD  1083 , is inputted to a CDS circuit  1085  of a video processing circuit  1084 , and after a signal component has been extracted, is inputted to Y/C separation circuit  1086 , and, in addition, is inputted to a luminance detection circuit  1087 . 
     The image-capturing signal, which was inputted to the Y/C separation circuit  1086 , is separated into a luminance signal Y and color difference signals Cr and Cb, and thereafter is inputted to a first matrix circuit  1088  and converted to an RGB signal. The RGB signal is inputted to a second matrix circuit  1089 , and converted to luminance signal Y and color difference signals R-Y and B-Y. 
     The luminance signal Y and color difference signals R-Y and B-Y are subjected to enlargement processing by an enlargement circuit  1090 , and thereafter are inputted to a highlighting circuit  1091 , where they undergo contour highlighting. After that, these signals are inputted to a third matrix circuit  1092  and converted to RGB signals (three primary color signals), and then outputted from an output terminal to a monitor not shown in the figure, and an endoscopic image of either an ordinary-light observation mode or a narrowband-light observation mode is displayed in color. 
     Further, the luminance detection circuit  1087  integrates an inputted CDS output signal and the like, computes an average value for the CDS output signal, generates a light modulation reference signal, and outputs a signal of the difference with the reference brightness value to the light-source apparatus  1081  as a modulated-light signal. Then, the light-source apparatus  1081  adjusts the quantity of illumination light in accordance with the modulated-light signal. 
     In the case of the synchronous system shown in  FIG. 35 , the disadvantage is the same as was explained in the case of the surface-sequential system, that is, it is difficult to properly modulate light at narrowband-light observation because a light modulation reference signal is generated by a common circuit configuration at ordinary-light observation and at narrowband-light observation. 
     In the second embodiment and in the third embodiment, which will be explained hereinbelow, an object is to provide an endoscope apparatus capable of properly modulating light during both ordinary-light observation and narrowband-light observation. 
     As shown in  FIG. 28 , an endoscope apparatus  1001  according to the second embodiment comprises an electronic endoscope (hereinafter, abbreviated simply as endoscope)  1002  for being inserted into a body cavity and performing an endoscopic examination; a light-source apparatus  1003  for supplying an illumination light to the endoscope  1002 ; a video processor  1004  for driving image-capturing means incorporated into the endoscope  1002 , and for performing signal processing to an output signal of image-capturing means; and a monitor  1005  for displaying an endoscopic image captured by image-capturing means in accordance with the inputting of a video signal outputted from the video processor  1004 . 
     The endoscope  1002  comprises a long, thin insertion unit  1007 ; an operation unit  1008  provided at the back end of the insertion unit  1007 ; and a universal cable  1009  extending from the operation unit  1008 . A light-guide connector  1011  at the distal end of the universal cable  1009  is detachably connected to the light-source apparatus  1003 , and a signal connector is detachably connected to the video processor  1004 . 
     A light guide  1013  for transmitting illumination light is inserted into the above-mentioned insertion unit  1007 , and illumination light from the light-source apparatus  1003  is supplied to the light guide  1013  by connecting a light-guide connector  1011  at the hand-side end of the light guide  1013  to the light-source apparatus  1003 . 
     The light-source apparatus  1003  emits white light (visible region) illumination light as ordinary illumination light when in the ordinary-light observation mode, and supplies to the light guide  1013 , and emits narrowband illumination light when in the narrowband-light observation mode, and supplies to the light guide  1013 . 
     Instructions for switching the ordinary-light observation mode and the narrowband-light observation mode, for example, can be carried out via a scope switch or other such mode-switching switch  1014  provided on the operation unit  1008  of the endoscope  1002 . Furthermore, the mode-switching switch  1014 , instead of being constituted as a scope switch provided on the endoscope  1002 , can also be constituted by a foot switch, can be provided on the front panel of the video processor  1004 , or can be constituted by a keyboard not shown in the figure. 
     A mode switching signal from the mode-switching switch  1014  is inputted to a control circuit  1015  inside the video processor  1004 , and when the mode switching signal is inputted, the control circuit  1015  selectively switches between ordinary illumination light and narrowband illumination light by controlling a filter insertion/removal mechanism  1016  of the light-source apparatus  1003 . 
     Further, as will be explained below, the control circuit  1015  can also implement control for switching a characteristic of the video signal processing system inside the video processor  1004  in response to the switching control of the illumination light supplied to the light guide  1013  from the light-source apparatus  3 . 
     The light-source apparatus  1003  is equipped with a lamp  1020 , which emits illumination light, and the lamp  1020  emits illumination light that covers the wavelength region of visible light (red, green and blue). The illumination light, subsequent to being made approximately white illumination light by cutting the infrared light via an infrared cutting filter  1021 , is irradiated onto a diaphragm  1022 . The size of the opening of the diaphragm  1022  is controlled by a diaphragm drive circuit  1023 . The amount of illumination light passing through the diaphragm  1022  is thereby controlled. 
     The illumination light passing through the diaphragm  1022  is irradiated onto a condenser lens  1025 , either by passing through a narrowband filter  1024  removably inserted into the illumination light path by the filter insertion/removal mechanism  1016  configured by a plunger or the like, or by not passing through the narrowband filter  1024 , is condensed by the condenser lens  1025 , and is irradiated onto the end face of the hand side of the light guide  1013 , that is, onto the incident end face. 
       FIG. 30  shows one example of the spectral characteristics of the narrowband filter  1024 . The narrowband filter  1024  exhibits trimodal filter characteristics, and, for example, comprises a narrowband transmittance filter characteristic portion Ra, Ga, Ba for each of the wavelength regions of red, green and blue. 
     More specifically, the narrowband transmittance filter characteristic portions Ra, Ga, Ba have bandpass characteristics in which the respective center wavelengths are 600 nm, 540 nm and 420 nm, and the full widths at half maximum are between 20 and 40 nm. 
     Therefore, when the narrowband filter  1024  is positioned in the illumination light path, a three-band narrowband illumination light that transmits the narrowband transmittance filter characteristic portions Ra, Ga, Ba is irradiated onto the light guide  1013 . 
     By contrast, when the narrowband filter  1024  is not positioned in the illumination light path, white light is supplied to the light guide  1013 . 
     Illumination light from the light guide  1013  is transmitted by the light guide  1013  to the distal end face thereof, passes through an illumination lens  1027  mounted to an illumination window provided on the distal end portion  1026  of the insertion unit  1007 , and is outputted to the outside, illuminating the surface of the living tissue of a diseased part or the like of a body cavity. 
     An observation window is provided adjacent to the illumination window in the distal end portion  1026 , and an objective lens  1028  is mounted to the observation window. The objective lens  1028  forms an optical image via the light reflected from the living tissue. A charge-coupled device (abbreviated CCD)  1029  is positioned at the image-forming location of the objective lens  1028  as a solid-state image-capturing device, and the image is subjected to photoelectric transfer by the CCD  1029 . 
     For example, the complementary color filter shown in  FIG. 29  is mounted in pixel units to the image-capturing surface of the CCD  1029  as a color separation filter  1030  for separating colors optically. 
     The four color chips of the complementary color filter, magenta (Mg), green (G), cyan (Cy) and yellow (Ye), are positioned in front of each pixel, with Mg and G being alternately arranged in the horizontal direction, and the arrays Mg, Cy, Mg, Ye and G, Ye, G, Cy being arranged in that order in the vertical direction. 
     Then, the CCD  1029 , which uses of the complementary color filter, is constituted so as to add and sequentially read out the two rows of pixels adjacent to one another in the vertical direction, reading out the rows of pixels by staggering the even and odd fields. As is known, luminance and color difference signals are then generated by the color separation circuit in the subsequent stage. 
     The above-mentioned CCD  1029  is connected to one end of a signal line, and connecting a signal connector, which is connected to the other end of the signal line, to the video processor  1004  connects a CCD drive circuit  1031  and CDS circuit  1032  inside the video processor  1004 . 
     The CCD  1029  inputs an image-capturing signal, which has undergone photoelectric transfer, to the CDS circuit  1032  in accordance with the application of a CCD drive signal from the CCD drive circuit  1031 . After a signal component has been extracted from the image-capturing signal, and converted to a baseband signal by the CDS circuit  1032 , the baseband signal is inputted to a Y/C separation/synchronization circuit  1033 , which performs Y/C separation and synchronization, and, in addition, is inputted to a selector  1035 , which constitutes a modulated-light signal generation circuit  1034  for generating a modulated-light signal, and to a light modulation circuit  1037  by way of an integration circuit  1036 . 
     The Y/C separation/synchronization circuit  1033 , subsequent to generating a luminance signal Y and a line-sequential color difference signal, passes these signals through a low-pass filter not shown in the figure to create a luminance signal Y and line-sequential color difference signal of a prescribed band. In addition, the Y/C separation/synchronization circuit  1033  utilizes a delay line or the like not shown in the figure to make the line-sequential color difference signal into synchronized color difference signals Cr (=2R−G) and Cb (=2B−G), and outputs these signals to a first matrix circuit  1038  together with the luminance signal Y. 
     Furthermore, when the observation mode is switched from the ordinary-light observation mode to the narrowband-light observation mode by operating the mode-switching switch  1014 , the control circuit  1015  changes the pass band of the low-pass filter through which the color difference signals Cr and Cb passed in the Y/C separation/synchronization circuit  1033  to broadband, thereby increasing the resolving power (resolution) thereof. 
     The first matrix circuit  1038  converts the inputted luminance signal Y and color difference signals Cr, Cb to color signals R, G and B, and outputs the converted color signals R, G, B to a second matrix circuit  1039 . 
     The first matrix circuit  1038  converts the inputted luminance signal Y and color difference signals Cr, Cb to color signals R, G, B, which are not mixed colors. 
     Further, the second matrix circuit  1039  converts the color signals R, G, B to a luminance signal Y and color difference signals R-Y and B-Y. 
     In this case, the second matrix circuit  1039  uses a known method to convert the color signals R, G, B to a luminance signal Y and color difference signals R-Y and B-Y when in the ordinary-light observation mode, but when in the narrowband-light observation mode, the control circuit  1015  changes a matrix coefficient, and carries out a conversion that increases the ratio of G and B color signals, which are short wavelengths, and more particularly the ratio of the shortest wavelength B color signals, relative to the long-wavelength R color signal. 
     In other words, when in the narrowband-light observation mode, the control circuit  1015  operates such that a luminance signal Ynbi and color difference signals R-Y and B-Y, which are weighted toward the B signal in particular, are generated from color signals R, G, B. 
     The conversion equation in this case is as follows when using three-row, three-column matrices A and K. 
     
       
         
           
             
               
                 
                   
                     ( 
                     
                       
                         
                           Ynbi 
                         
                       
                       
                         
                           
                             R 
                             - 
                             Y 
                           
                         
                       
                       
                         
                           
                             B 
                             - 
                             Y 
                           
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       A 
                       ⁡ 
                       
                         ( 
                         
                           
                             
                               0 
                             
                             
                               
                                 k 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             
                               0 
                             
                           
                           
                             
                               0 
                             
                             
                               0 
                             
                             
                               
                                 k 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                               
                             
                           
                           
                             
                               0 
                             
                             
                               0 
                             
                             
                               
                                 k 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 3 
                               
                             
                           
                         
                         ) 
                       
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           
                             R 
                           
                         
                         
                           
                             G 
                           
                         
                         
                           
                             B 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     Here, matrix K, for example, comprises three real coefficients k1 through k3 (the other coefficient component is 0), and, a conversion equation like Equation (2) suppresses the long-wavelength R color signal, and, by contrast, increases the weight of the short-wavelength G and B color signals. Furthermore, when in the ordinary-light observation mode, conversion is carried out omitting the matrix K in Equation (2). 
     Further, A is a matrix for converting from RGB signals to Y color difference signals, and the following known operation coefficient (3) can be used. 
     
       
         
           
             
               
                 
                   A 
                   = 
                   
                     ( 
                     
                       
                         
                           0.299 
                         
                         
                           0.587 
                         
                         
                           0.114 
                         
                       
                       
                         
                           
                             - 
                             0.299 
                           
                         
                         
                           
                             - 
                             0.587 
                           
                         
                         
                           0.886 
                         
                       
                       
                         
                           0.701 
                         
                         
                           
                             - 
                             0.587 
                           
                         
                         
                           
                             - 
                             0.114 
                           
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     The luminance signal Y and color difference signals R-Y and B-Y outputted from the second matrix circuit  1039  are inputted to an enlargement circuit  1040 , and are subjected to enlargement processing. Further, the luminance signal Y is inputted to the selector  1035 . 
     The output signal of the enlargement circuit  1040  is inputted to a highlighting circuit  1041 , and subjected to structural highlight processing. The output signal of this highlighting circuit  1041  is inputted to a third matrix circuit  1042 . Furthermore, the luminance signal Y component alone can be highlighted by the highlighting circuit  1041 . 
     The luminance signal Y and color difference signals R-Y and B-Y inputted to the third matrix circuit  1042  are converted to color signals R, G, B by the third matrix circuit  1042 , and outputted to the monitor  1005  from an output terminal. Then, the endoscopic image captured by the CCD  1029  is displayed on the display screen of the monitor  1005 . 
     The above-mentioned control circuit  1015  controls signal selection by the selector  1035  using a mode switching signal. 
     More specifically, when switching to the narrowband-light observation mode, the control circuit  1015  implements switching such that the luminance signal Y outputted from the second matrix circuit  1039  is inputted to the integration circuit  1036  and light modulation circuit  1037  by way of the selector  1035 . Furthermore, the integration circuit  1036 , which integrates an input signal and outputs an average value, can also be an equalization circuit for generating an average value. 
     Meanwhile, in the ordinary-light observation mode, the control circuit  1015  implements switching such that an output signal from the CDS circuit  1032  is inputted to the integration circuit  1036  and light modulation circuit  1037  by way of the selector  1035 . 
     The configuration of the modulated-light signal generation circuit  1034  will be explained below in accordance with  FIG. 31 . In the present embodiment, the modulated-light signal generation circuit  1034  equalizes an output signal of the CDS circuit  1032  and generates a light modulation reference signal &lt;Yn&gt; in the ordinary-light observation mode, and equalizes a luminance signal outputted by way of the second matrix circuit  1039 , and generates a light modulation reference signal &lt;Ynbi&gt; in the narrowband-light observation mode. 
     In the narrowband-light observation mode, the ratio of respective color signals in the light modulation reference signal &lt;Ynbi&gt; differs from the ratio of respective color signals in the light modulation reference signal &lt;Yn&gt; resulting from the second matrix circuit  1039  implementing a conversion and the like that increases the ratio of a short-wavelength color signal. 
       FIG. 31  shows an example of a configuration of the modulated-light signal generating circuit  1034 . 
     As explained hereinabove, a signal selected by the selector  1035  is inputted to the integration circuit  1036 , where it becomes a light modulation reference signal of either &lt;Yn&gt; or &lt;Ynbi&gt; (notated as &lt;Yn&gt;/&lt;Ynbi&gt; in this specification and drawings), which has undergone integration and equalization in a prescribed period, and is inputted to a subtraction circuit  1045 , which constitutes a light modulation circuit  1037 . Furthermore, the integration circuit  1036  is equipped with a S/H circuit, which performs sample/hold (S/H), and outputs to the subtraction circuit  1045  an integration value integrated in a prescribed period by an S/H control signal Ssh from the control circuit  1015 . 
     The subtraction circuit  1045  outputs to the diaphragm drive circuit  1023  of the light-source apparatus  1003 , as a modulated-light signal, a value arrived at by subtracting from the light modulation reference signal &lt;Yn&gt;/&lt;Ynbi&gt; a reference value (a light modulation target value) En/Enbi corresponding to the proper brightness generated by a reference value generation circuit (target value generation circuit)  1046 . 
     Furthermore, En is the reference value in the ordinary-light observation mode, and Enbi is the reference value in the narrowband-light observation mode. Respectively setting such target values, which constitute light modulation references, in the ordinary-light observation mode and in the narrowband-light observation mode makes it possible to modulate light to an appropriate target value in both modes. 
     In this case, the control circuit  1015 , operating in response to a mode-switching signal, uses a switching control signal Sc to switch between the selector  1035  and the reference value En/Enbi. Further, the control circuit  1015  applies to the integration circuit  1036  a control signal Ssh, which performs sample/hold, and outputs to the subtraction circuit  1045  a light modulation reference signal &lt;Yn&gt;/&lt;Ynbi&gt; that has been integrated in a prescribed period. 
     The modulated-light signal outputted from the light modulation circuit  1037  is outputted to the diaphragm drive circuit  1023 . 
     The diaphragm drive circuit  1023  reduces the size of the opening of the diaphragm  1022  when the modulated-light signal is a positive value, for example, and, conversely, increases the size of the opening of the diaphragm  1022  when the modulated-light signal is a negative value, and adjusts the quantity of illumination light, automatically modulating the light such that the light modulation reference signal &lt;Yn&gt;/&lt;Ynbi&gt; constitutes a reference value En/Enbi of proper brightness. 
     The automatic light modulation makes it possible for an endoscopic image captured by the CCD  1029  and displayed on the monitor  1005  to constantly maintain the proper brightness. 
     Furthermore, three primary color signals R, G, B actually inputted to the respective R, G, B channels of the monitor  1005  from the video signal output terminal constitute the signals G, B, B (weighting differs according to the coefficients) when Equation (1) is employed in the narrowband-light observation mode, the ratio of B signals in particular increases, and thanks to the B signals, it becomes possible to display, under easy-to-identify circumstances, an endoscopic image corresponding to a structure, such as the capillary vessels in the vicinity of a superficial portion of a living tissue. 
     That is, the signals respectively inputted to the R, G, B channels of the monitor  1005  in the narrowband-light observation mode are actually G, B, and B signals, thereby enhancing visibility. 
     Operation according to the present embodiment will be explained below by referring to  FIG. 32 . 
     An operator connects an endoscope  1002  to a light-source apparatus  1003  and video processor  1004  as shown in  FIG. 28 , turns on the power, and the control circuit  1015  of the video processor  1004  starts initialization processing, and as shown in Step S 1 , for example, sets the ordinary-light observation mode as the operation mode of the light-source apparatus  1003  and video processor  1004 . 
     In this state, the light-source apparatus  1003  is set such that the narrowband filter  1024  is separated from the illumination light path as shown in  FIG. 28 , and image capturing is performed by the endoscope  1002  under white illumination light. Further, the respective parts of the video processor  1004  are also set to perform signal processing in the ordinary-light observation mode state. 
     In this case, the control circuit  1015  controls the signal switching of the selector  1035  such that an output signal from the CDS circuit  1032  is inputted to the integration circuit  1036 . Then, the control circuit  1015  implements control so as to generate a light modulation reference signal &lt;Yn&gt; in accordance with an output signal of the CDS circuit  1032 , and, in addition, to send a modulated-light signal, from which a brightness reference value En has been subtracted by the light modulation circuit  1037 , to the diaphragm drive circuit  1023  of the light-source apparatus  1003 , such that the diaphragm  1022  constitutes the appropriate quantity of illumination light. 
     An operator inserts the insertion unit  1007  of the endoscope  1002  into a body cavity of a patient, making it possible to conduct an endoscopic examination in a state of illumination under which an image of appropriate brightness can be obtained. When he wants to observe in more detail the location or course of the surface blood vessels of a tissue targeted for examination, such as a diseased part of the body cavity, the operator operates the mode-switching switch  1014 . 
     As shown in step S 2 , the control circuit  1015  monitors whether or not the mode-switching switch  1014  has been operated, and when the mode-switching switch  1014  has not been operated, it maintains this status, and when the mode-switching switch  1014  has been operated, it proceeds to the next step S 3 . 
     In step S 3 , the control circuit  1015  changes the operation mode of the light-source apparatus  1003  and video processor  1004  to the setting state of the narrowband-light observation mode. 
     More specifically, the control circuit  1015  performs control relative to the light-source apparatus  1003  such that the narrowband filter  1024  is positioned in the illumination light path as indicated by the two-dot chain line in  FIG. 28 . As indicated by the transmittance characteristics shown in  FIG. 30 , positioning the narrowband filter  1024  in the path of the illumination light results in illumination by a narrowband illumination light in accordance with the narrowband transmission filter characteristic sections Ra, Ga, Ba. 
     Further, the control circuit  1015  changes the settings of the respective parts of the video processor  1004 . More specifically, the control circuit  1015  implements changes so as to increase a matrix coefficient of the second matrix circuit  1039 , and more particularly the ratio of signal components resulting from the color signal B (in accordance with the narrowband transmission filter characteristic section Ba) in the luminance signal Ynbi. 
     Further, the control circuit  1015  switches the selector  1035 , and a luminance signal Ynbi from the second matrix circuit  1039  is inputted to the integration circuit  1036  by way of the selector  1035 , becoming the light modulation reference signal &lt;Ynbi&gt;, and, in addition, the light modulation circuit  1037  subtracts the brightness reference value Enbi and generates a modulated-light signal. This modulated-light signal adjusts the quantity of illumination light. Then, an appropriate quantity of illumination light for facilitating a diagnosis is set in the narrowband-light observation mode. 
     Further, since changing the settings of the above-mentioned signal processing system implements changes that increase, for example, a matrix coefficient of the second matrix circuit  1039  in the narrowband light observation mode, and more particularly the ratio of signal components of the color signal B, it is possible to observe in an easy-to-identify state the course of a capillary vessel in the vicinity of a superficial portion of a living tissue, the image of which was captured under B illumination light via the narrowband transmission filter characteristic section Ba. 
     Further, since narrowband properties are converted to broadband when color difference signals Cr, Cb are generated in the Y/C separation/synchronization circuit  1033 , it is possible to enhance the resolution of the course of a capillary vessel, as well as the course of a blood vessel located deeper than the superficial portion, the image of which was captured under G illumination light via the narrowband transmission filter characteristic section Ga. 
     In the next step S 4 , the control circuit  1015  monitors whether or not the mode-switching switch  1014  has been operated, and when the mode-switching switch  1014  has not been operated, maintains the status, and when the mode-switching switch  1014  has been operated, returns to the next step S 1 . 
     According to an embodiment like this, a modulated-light signal suited to light modulation is generated from respective luminance signals in the ordinary-light observation mode and the narrowband-light observation mode, thereby producing an endoscopic image of a brightness well suited to each mode of observation. 
     Further, according to the present embodiment, it is possible to adequately secure the observation function of the narrowband-light observation mode by holding a color image-capturing function resulting from an ordinary synchronous system, and by changing a coefficient and other settings of the respective parts of the video processor  1004  in the narrowband-light observation mode as well. 
     Next, a concrete example for appropriately setting, in both the ordinary-light observation mode and narrowband-light observation mode, the ratio of the contribution of the respective color signals that generate a light modulation reference signal, will be explained. 
       FIG. 33  shows a configuration of the peripheral parts of modulated-light signal generation circuit  1034 B in a variation of the present embodiment. In the modulated-light signal generation circuit  1034 B, color signals R, G, B of the first matrix circuit  1038  are inputted into respective multipliers  1047   a ,  1047   b , and  1047   c , and after being respectively multiplied by coefficients outputted from a ROM  1048 , which stores multiplier coefficients, are added by an addition circuit  1049 . 
     The ROM  1048  stores coefficients for the ordinary-light observation mode, and coefficients for the narrowband-light observation mode, and the control circuit  1015 , operating in response to a mode-switching signal, reads out the corresponding coefficients, and outputs to the multipliers  1047   a ,  1047   b ,  1047   c.    
     More specifically, in the ordinary-light observation mode, coefficients of a ratio of 5:9:3 (when equalized, this ratio becomes 5/17:9/17:3/17) are inputted to the multipliers  1047   a ,  1047   b ,  1047   c  from the ROM  1048 , and subsequent to being respectively multiplied with R, G, B color signals, these coefficients are added by the addition circuit  1049 . 
     Therefore, the light modulation reference signal Yn, prior to being outputted from the addition circuit  1049  and equalized in the ordinary-light observation mode, constitutes Yn=5R/17+9G/17+3B/17. 
     Further, in the narrowband-light observation mode, coefficients of a ratio of 0:5:12 (when equalized, this ratio becomes 0/17:5/17:12/17) are inputted to the multipliers  1047   a ,  1047   b ,  1047   c  from the ROM  1048 , and subsequent to being respectively multiplied with R, G, B color signals, these coefficients are added by the addition circuit  1049 . 
     Therefore, the light modulation reference signal Ynbi, prior to being outputted from the addition circuit  49  and equalized in the narrowband-light observation mode, constitutes Ynbi=0×R/17+5G/17+12B/17. Thus, the output signal Yn or Ynbi (that is, Yn/Ynbi) of the addition circuit  1049  is inputted to the integration circuit  1036 , is integrated, respectively become a light modulation reference signal &lt;Yn&gt;/&lt;Ynbi&gt;, and is inputted to the light modulation circuit  1037 . 
     The rest of the configuration is the same as that of the second embodiment. 
     According to this variation, since the configuration is such that the ratio of color signals is appropriately set, and a light modulation reference signal is generated in both the ordinary-light observation mode and the narrowband-light observation mode just like in the second embodiment, it is possible to achieve an image of a brightness that facilitates a diagnosis in each mode. 
     Furthermore, as described hereinabove, since signal processing, which suppresses the R color signal via the narrowband transmission filter section Ra in the narrowband-light observation mode is performed, a narrowband filter that does not have the transmittance characteristics of the narrowband transmission filter section Ra can be used as the narrowband filter  1024  shown in  FIG. 30 . In this case, the narrowband filter constitutes a two-peak filter having the narrowband transmission filter sections Ga and Ba, and can contribute toward lowering costs. 
     Third Embodiment 
     Next, a third embodiment of the present invention will be explained by referring to  FIGS. 36 through 39 . Since the third embodiment is practically the same as the second embodiment, only the points of difference will be explained, and an explanation of identical components having the same reference numerals will be omitted. 
       FIG. 36  shows a configuration of an endoscope apparatus  101 B according to a third embodiment of the present invention. The second embodiment is a synchronous-type endoscope apparatus  1001 , which captures a color image using a synchronous-type endoscope  1002  including a color filter (optical filter for color separation), but the present embodiment is a surface-sequential-type endoscope apparatus  1001 B, which surface-sequentially captures a color image using a surface-sequential-type endoscope  1002 B that does not have a color filter. 
     As shown in  FIG. 36 , the endoscope apparatus  1001 B comprises an endoscope  1002 B; a light-source apparatus  1003 B for supplying illumination light to the endoscope  1002 B; a video processor  1004 B, which drives image-capturing means built into the endoscope  1002 B, and performs signal processing for image-capturing means output signals; and a monitor  1005 , which displays an endoscopic image captured by image-capturing means in accordance with the inputting of a video signal outputted from the video processor  1004 B. 
     The endoscope  1002 B employs a CCD  1029  that does not have a color separation filter  1030 , in other words, a monochrome CCD, instead of the color separation filter  1030 -equipped CCD  1029  in the endoscope  1002  of  FIG. 28 . 
     Further, the light-source apparatus  1003 B has a rotating filter  1051  arranged in the optical path between, for example, the diaphragm  1022  and filter  1024  in the endoscope  1003  of  FIG. 28 , and the rotating filter  1051  is rotated at a constant speed by a motor  1052 . 
     R, G and B filters  1053 R,  1053 G,  1053 B which respectively transmit light of the respective bands of R, G, B, are circumferentially mounted to the rotating filter  1051  as shown in  FIG. 37(A) . The transmittance characteristics of these R, G, B filters  1053 R,  1053 G,  1053 B comprise transmission sections Rb, Gb, Bb, which transmit the respective R, G, B wavelength regions in broadband as shown in  FIG. 37(B) . 
     Then, in the ordinary-light observation mode, the broadband R, G, B illumination light, which permeates the R, G, B filters  1053 R,  1053 G,  1053 B of the rotating filter  1051 , is surface-sequentially supplied to the light guide  1013 . 
     Meanwhile, in the narrowband-light observation mode, the narrowband filter  1024  is arranged in the optical path, and the broadband R, G, B illumination light, which permeates the R, G, B filters  1053 R,  1053 G,  1053 B of the rotating filter  1051 , is made into narrowband R, G, B illumination light by the narrowband filter  1024 , and surface-sequentially supplied to the light guide  1013 . 
     Further, in the video processor  1004 B of the present embodiment, the CCD  1029  is driven by the CCD drive circuit  1031 , and an image-capturing signal captured by the CCD  1029  is inputted to the CDS circuit  1032 , and subjected to CDS processing. 
     The output signal of the CDS circuit  1032  is inputted to an A/D conversion circuit  1054 , and converted to a digital signal, and, in addition, is inputted to a light modulation circuit  1057  by way of a detection circuit  1056 , which constitutes a modulated-light signal generation circuit  1055 . 
     A digital signal generated by the A/D conversion circuit  1054  is inputted to a synchronization circuit  1058 , and after surface-sequentially captured R, G, B color component images are temporarily stored in a memory constituting the synchronization circuit  1058 , R, G, B signals, which have been simultaneously read out and synchronized, are outputted to a matrix circuit  1059 . 
     A matrix coefficient of the matrix circuit  1059  is changed in the ordinary-light observation mode and in narrowband-light observation mode by the control circuit  1015 . More specifically, in the ordinary-light observation mode, it is a matrix of units, but in the narrowband-light observation mode, the matrix coefficient is changed so as to possess a function similar to that of the second matrix circuit  1039  of the second embodiment. 
     An output signal of the matrix circuit  1059  is outputted to the monitor  1005  from an output terminal after respectively undergoing enlargement and highlight processing by the enlargement circuit  1040  and highlighting circuit  1041  the same as in the second embodiment. 
       FIG. 38  shows an example of the circuitry of the modulated-light signal generation circuit  1055 . Surface-sequential R, G, B signals are inputted, for example, to a gain control amplifier (abbreviated GCA)  1061 , which constitutes the detection circuit  1056 , and a gain control signal Sgc from the control circuit  1015  is applied to a gain control terminal of the GCA  1061 . The GCA  1061  has the gain (amplification factor) at output by amplifying an input signal variably controlled in accordance with the signal level of the gain control signal Sgc. 
     The gain control signal Sgc changes each signal period of a surface-sequential input signal, and in the ordinary-light observation mode, for example, the gain of the GCA  1061  is set, for example, at the ratio 5:9:3 relative to R, G, B input signals. The ratio setting when equalized (standardized) becomes 5/17:9/17:3/17. 
     Meanwhile, in the narrowband-light observation mode, for example, the gain of the GCA  1061  is set, for example, at the ratio 0:5:12 relative to the R, G, B input signals. The ratio setting when equalized becomes 0/17:5/17:12/17. 
     Further, an output signal of the above-mentioned GCA  1061  is inputted to the integration circuit  1036 , where it is integrated, and a light modulation reference signal &lt;Yn&gt;/&lt;Ynbi&gt; is generated. 
     In the ordinary-light observation mode, the light modulation reference signal &lt;Yn&gt; becomes &lt;Yn&gt;=5&lt;R&gt;/17+9&lt;G&gt;/17+3&lt;B&gt;/17. 
     Further, in the narrowband-light observation mode, the light modulation reference signal &lt;Ynbi&gt; becomes &lt;Ynbi&gt;=0 x&lt;R&gt;/17+5&lt;G&gt;/17+12&lt;B&gt;/17. 
     The light modulation reference signal &lt;Yn&gt;/&lt;Ynbi&gt; outputted from the integration circuit  1036  is inputted to the subtraction circuit  1045 , which constitutes a light modulation circuit  1057 , and a signal, from which reference values En/Enbi of the reference value generation circuit  1046  have been subtracted, is outputted to the diaphragm drive circuit  1023  as a modulated-light signal. 
     Further, a reference value E is also variably set corresponding to the ordinary-light observation mode and the narrowband-light observation mode by a switching control signal Sc from the control circuit  1015 . 
     Furthermore, the detection circuit  1056  may be constituted from a multiplier and a coefficient unit. 
     According to the present embodiment, which has a configuration and operations like this, it is possible to automatically adjust the quantity of illumination light appropriately in both the ordinary-light observation mode and in the narrowband-light observation mode the same as in the variation of the second embodiment. 
       FIG. 39  shows a configuration of a video processor  1004 C of a variation of the third embodiment. The video processor  1004 C applies the modulated-light signal generation circuit  1034  in the second embodiment, which is a synchronous-type, and comprises a surface-sequential-type modulated-light signal generation circuit  1034 C, which is similar to the modulated-light signal generation circuit  1034 . 
     Thus, the video processor  1004 C employs the second matrix circuit  1039  of the second embodiment instead of the matrix circuit  1059  in the video processor  1004 B of  FIG. 36 . The second matrix circuit  1039  converts R, G, B signals outputted from a synchronization circuit  1058  to a luminance signal Y and color difference signals R-Y, B-Y. 
     In this case, the matrix coefficients of the second matrix circuit  1039  are linked to mode switching and are switched by the control circuit  1015  as in the second embodiment. 
     That is, in the ordinary-light observation mode, the second matrix circuit  1039  converts an RGB signal to a luminance signal Y and color difference signals R-Y, B-Y, but in the narrowband-light observation mode, conversion is performed as in Equation (2) explained in the second embodiment. 
     Then, the luminance signal Ynbi in the narrowband-light observation mode is integrated by the integration circuit  1036  by way of the selector  1035 , which constitutes the modulated-light signal generation circuit  1034 C, to become light modulation reference signal &lt;Ynbi&gt;, which is inputted to the light modulation circuit  1037  and becomes a modulated-light signal. 
     Further, in the ordinary-light observation mode, an output signal of the CDS circuit  1032  is integrated by the integration circuit  1036  by way of the selector  1035 , which constitutes the modulated-light signal generation circuit  1034 C, to become light modulation reference signal &lt;Yn&gt;, which is inputted to the light modulation circuit  1037  and becomes a modulated-light signal. 
     Furthermore, an output signal of the highlighting circuit  1041  is inputted to the third matrix circuit  1042 , and subsequent to being converted to a color signal RGB, is outputted to the monitor  1005  from an output terminal. 
     According to a variation of the third embodiment constituted like this, it is a surface-sequential system, but the same operational effect as that of the second embodiment can be obtained. 
     Furthermore, for example, a two-peak filter, which comprises the narrowband transmission filter characteristic sections Ga, Ba, but does not comprise the transmittance characteristics of the narrowband transmission filter characteristic section Ra as explained in the second embodiment, can also be used in the third embodiment as the narrowband filter  1024 . 
     Fourth Embodiment 
       FIGS. 40 through 48  are related to a fourth embodiment of the present invention.  FIG. 40  shows a configuration of an endoscope apparatus according to a fourth embodiment of the present invention;  FIG. 41  shows a configuration of a filter array of color separating filters provided in a solid-state image-capturing device;  FIG. 42  shows an example of the spectral characteristics of a narrowband filter;  FIG. 43  shows a flowchart used for explaining the operation of the present embodiment;  FIG. 44  shows the signal bands in a luminance signal and color difference signals;  FIG. 45  shows the coefficients of a second matrix circuit set in a first variation that takes into account the characteristics of  FIG. 44 ;  FIG. 46  shows the spectral characteristics of a narrowband filter in a second variation;  FIG. 47  shows the coefficient of the second matrix circuit set in the second variation of  FIG. 46 ; and  FIG. 48  shows a block diagram depicting a configuration of a video signal processing apparatus of the prior art. 
     In recent years, electronic endoscopes including image-capturing means have come to be widely employed in various types of endoscopic examinations. 
     When performing an endoscopic examination using an electronic endoscope, there is a synchronous-type endoscope apparatus, which captures a color image under white light by using an image-capturing device including a color optical filter, and there is a surface-sequential-type endoscope apparatus, which generates a color image by using a monochrome image-capturing device, and respectively capturing an image under R, G and B surface-sequential illumination lights. The signal processing system differs in the two types of apparatuses. 
     Further, for example, Japan Patent Laid-open No. 2002-95635 discloses a endoscope apparatus, which uses narrowband illumination light, and which can display, as readily identifiable image data, the state of a blood vessel&#39;s course in the depth direction in the vicinity of a superficial portion of a mucous membrane. Such data can be easily buried in optical data obtained with ordinary visible light. 
     In the prior art of the above-mentioned official gazette, a narrowband image is surface-sequentially generated using a narrowband illumination light, making it possible to obtain a narrowband image relatively easily without having to make a big change in the signal processing system, if the illumination light is changed to narrowband illumination light instead of R, G, B surface-sequential illumination light. 
     Meanwhile,  FIG. 48  shows a configuration of a video signal processing apparatus  2081  for a synchronous-type electronic endoscope of the prior art. 
     A color image-capturing signal captured by a charge-coupled device (abbreviated CCD)  2083 , which comprises a color separation filter  2082 , is inputted to a CDS circuit  2084  inside the video signal processing apparatus  2081 , where it is subjected to CDS processing, and a baseband signal component is extracted. 
     An output signal of the CDS circuit  2084  is inputted to an A/D conversion circuit  2085 , where it is converted from an analog signal to a digital signal. The digital signal is inputted to a Y/C separation circuit  2086 , and is separated into a luminance signal Y and a line-sequential color signal (color difference signal) C in the Y/C separation circuit  2086 . 
     The luminance signal Y is inputted to a selector  2088  by way of a γ circuit  2087  (this luminance signal becomes Yh), and, in addition, is inputted to a first low-pass filter (abbreviated LPF)  2089 . The LPF  2089  is set to broadband, and the luminance signal Y 1  of the band set by the LPF  2089  is inputted to a first matrix circuit  2090 . 
     Further, the color signal C is inputted to a (line-sequential) synchronization circuit  2092  by way of a second LPF  2091 . In this case, the second LPF  2091  is a lower band than the first LPF  2089 . 
     The synchronization circuit  2092  generates synchronized color difference signals Cr (=2R−G) and Cb (=2B−G), and inputs the color difference signals Cr, Cb to the first matrix circuit  2090 . 
     The first matrix circuit  2090  converts the luminance signal Y 1  and color difference signals Cr, Cb to three primary color signals R 1 , G 1 , B 1 , and outputs them to a γ circuit  2093 . The three primary color signals R 2 , G 2 , B 2 , which have been subjected to γ-correction by the γ circuit  2093 , are inputted to a second matrix circuit  2094 , and are converted to a luminance signal Ynbi and color difference signals R-Y, B-Y by the second matrix circuit  2094 . 
     In this case, the second matrix circuit  2094  converts the three primary color signals R 2 , G 2 , B 2  to the luminance signal Ynbi and color difference signals R-Y and B-Y so that the color constitutes a natural tone. 
     The luminance signal Ynbi outputted by the second matrix circuit  2094  is inputted to an enlargement circuit  2095  by way of the selector  2088 , and the color difference signals R-Y, B-Y are inputted to the enlargement circuit  2095 . The selector  2088  selects the γ-corrected luminance signal Yh from the Y/C separation circuit  2086 , and the luminance signal Ynbi inputted by way of the second matrix circuit  2094 , and outputs them to the enlargement circuit  2095 . 
     The luminance signal Yh/Ynbi, which was subjected to enlargement processing by the enlargement circuit  2095 , is inputted to a third matrix circuit  2097  by way of a highlighting circuit  2096 , and the color difference signals R-Y, B-Y, which were subjected to enlargement processing by the enlargement circuit  2095 , are inputted to the third matrix circuit  2097  without going through the highlighting circuit  2096 . 
     Then, by the third matrix circuit  2097 , conversion to three primary color signals R, G, B is carried out, and output to a color monitor not shown in the figure is performed. 
     Furthermore, the selector  2088  selects the luminance signal Yh at ordinary light observation via ordinary light, and selects the luminance signal that passed through the second matrix circuit  2094 , that is, the luminance signal Ynbi, at narrowband-light observation via the illumination of narrowband light. 
     In the conventional video signal processing apparatus  2081 , since signal processing that conforms to specifications of a standard video signal is carried out, broadband signal processing is implemented for the luminance signal Y, and low-band signal processing is implemented for the color signal C. 
     In the prior art shown in  FIG. 48 , image quality is ensured in ordinary-light observation, but the drawback is that the color signal C is processed as a low-band color signal in narrowband light observation, resulting in an image with low resolution. 
     Furthermore, because the illumination light is made narrowband at narrowband-light observation (NBI observation), the observation image becomes dark. 
     With the foregoing in mind, an object of the present embodiment and the fifth embodiment, which will be explained hereinbelow, is to provide an endoscope apparatus that can support ordinary-light observation, and achieve a good quality endoscopic image during narrowband-light observations as well. 
     An endoscope apparatus  2001  according to a fourth embodiment, as shown in  FIG. 40 , comprises an electronic endoscope (hereinafter, abbreviated as simply endoscope)  2002 , which is inserted into a body cavity, and which carries out an endoscopic examination; a light-source apparatus  2003 , which supplies illumination light to the endoscope  2002 ; a video processor  2004  as an endoscopic video signal processing unit, which drives image capturing means built into the endoscope  2002 , and carries out signal processing relative to an output signal of image-capturing means; and a monitor  2005 , which, in accordance with being inputted with a video signal outputted from the video processor  2004 , displays an endoscopic image captured by image-capturing means. 
     The endoscope  2002  comprises a long, thin insertion unit  2007 ; an operation unit  2008 , which is disposed at the back end of the insertion unit  2007 ; and a universal cable  2009 , which extends from the operation unit  2008 , and a light-guide connector  2011  at the end of the universal cable  2009  is removably connected to the light-source apparatus  2003 , and a signal connector is removably connected to the video processor  2004 . 
     A light guide  2013 , which transmits illumination light, is inserted into the above-mentioned insertion unit  2007 , and illumination light from the light-source apparatus  2003  is supplied to the light guide  2013  by connecting the light-guide connector  2011  of the light-source apparatus  2003  end of the light guide  2013  to the light-source apparatus  2003 . 
     The light-source apparatus  2003  generates an illumination light of white light (visible region) as the ordinary illumination light in the ordinary-light observation mode, and supplies same to the light guide  2013 , and generates narrowband illumination light in the narrowband-light observation mode, and supplies to the light guide  2013 . 
     Switching instructions of the ordinary-light observation mode and narrowband-light observation mode, for example, can be executed by a scope switch or other such mode-switching switch  2014  provided to the operation unit  2008  of the endoscope  2002 . Furthermore, in addition to being constituted by a scope switch provided to the endoscope  2002 , the mode-switching switch  2014  can also be constituted by a foot switch, can be provided on the front panel of the video processor  2004 , and can also be constituted by a keyboard not shown in the figure. 
     A switching signal from the mode-switching switch  2014  is inputted to the control circuit  2015  inside the video processor  2004 , and when a switching signal is inputted, the control circuit  2015  controls the filter insertion/removal mechanism  2016  of the light-source apparatus  2003 , and selectively switches between an ordinary illumination light and a narrowband illumination light. 
     Further, as will be explained hereinbelow, the control circuit  2015  operates in response to the switching control of the illumination light supplied to the light guide  2013  from the light-source apparatus  2003 , and also executes control for switching the characteristics of the video signal processing system in the video processor  2004 . Then, the control circuit  2015  is able to carry out signal processing respectively suitable for the ordinary-light observation mode and the narrowband-light observation mode by switching the characteristics of the video signal processing system by a switch operation via the mode-switching switch  2014 . 
     The light-source apparatus  2003  is equipped with a lamp  2020  for generating an illumination light, and the lamp  2020  generates an illumination light including the visible light region. The illumination light, subsequent to having infrared light cut by an infrared cutting filter  2021 , and being made into illumination light approaching a wavelength band of approximate white light, is irradiated onto a diaphragm  2022 . The size of the opening of the diaphragm  2022  is adjusted by a diaphragm drive circuit  2023 , thereby controlling the quantity of light passing therethrough. 
     The illumination light that has passed through the diaphragm  2022  either passes through a narrowband filter  2024 , which is removably inserted into the illumination light path by the filter insertion/removal mechanism  2016  constituting a plunger or the like (in the narrowband-light observation mode), or does not pass through the narrowband filter  2024  (in the ordinary-light observation mode), is irradiated onto a condenser lens  2025 , is condensed by the condenser lens  2025 , and is irradiated onto the hand-side end face of the light guide  2013 , that is, the incident end face. 
       FIG. 41  shows one example of the spectral characteristics of the narrowband filter  2024 . The narrowband filter  2024  exhibits three-peak filter characteristics, and, for example, has the respective narrowband transmission filter characteristic sections Ra, Ga, Ba in the respective wavelength regions of red, green and blue. 
     More specifically, the narrowband transmission filter characteristic sections Ra, Ga, Ba have bandpass characteristics in which the respective center wavelengths are 600 nm, 540 nm and 420 nm, and the full widths at half maximum thereof are between 20 nm and 40 nm. 
     Therefore, when the narrowband filter  2024  is positioned in the illumination light path, three bands of narrowband illumination light, which permeate the narrowband transmission filter characteristic sections Ra, Ga, Ba, are irradiated into the light guide  2013 . 
     By contrast, when the narrowband filter  2024  is not positioned in the illumination light path, white light is supplied to the light guide  2013 . 
     The illumination light from the light guide  2013  is transmitted by the light guide  2013  to the distal end face thereof, and is outputted to the outside by way of an illumination lens  2027  mounted to an illumination window provided at the distal end face  2026  of the insertion unit  2007 , and illuminates the surface of living tissue inside a patient&#39;s body cavity. 
     An observation window is provided adjacent to the illumination window in the distal end face  2026 , and an objective lens  2028  is mounted to the observation window. The objective lens  2028  provides an optical image by reflected light from the living tissue. A charge-coupled device (abbreviated CCD)  2029  is arranged as a solid-state image-capturing device at the imaging location of the objective lens  2028 , and the CCD  2029  performs photoelectric transfer. 
     For example, the complementary color filter shown in  FIG. 42  is mounted in pixel units to the image-capturing surface of the CCD  2029  as a color separation filter  2030  for separating colors optically. 
     The four color chips of the complementary color filter, magenta (Mg), green (G), cyan (Cy) and yellow (Ye), are positioned in front of each pixel, with Mg and G being alternately arranged in the horizontal direction, and the arrays Mg, Cy, Mg, Ye and G, Ye, G, Cy being arranged in that order in the vertical direction. 
     Then, the CCD  2029 , which uses the complementary color filter, is constituted so as to add and sequentially read out the two rows of pixels adjacent to one another in the vertical direction, reading out the rows of pixels by staggering the even and odd fields. As is known, luminance and color difference signals are then generated by the color separation circuit in the subsequent stage. 
     The above-mentioned CCD  2029  is connected to one end of a signal line, and by connecting a signal connector, which is connected to the other end of the signal line, to the video processor  2004 , CCD  2029  is connected to a CCD drive circuit  2031  and CDS circuit  2032  inside the video processor  2004 . 
     Furthermore, each endoscope  2002  comprises an ID generation unit  2033 , which generates specific identification information (ID) to the endoscope  2002 , and an ID by the ID generation unit  2033  is inputted to the control circuit  2015 , and the control circuit  2015  uses the ID to identify the type of endoscope  2002  connected to the video processor  2004 , and the number and type of pixels of the CCD  2029  built into the endoscope  2002 . 
     Then, the control circuit  2015  controls a CCD drive circuit  2031  so as to properly drive the CCD  2029  of the identified endoscope  2002 . 
     The CCD  2029  inputs an image-capturing signal, which has undergone photoelectric transfer, to correlated double sampling circuit (abbreviated CDS circuit)  2032  in accordance with the application of a CCD drive signal from the CCD drive circuit  2031 . After a signal component has been extracted from the image-capturing signal and converted to a baseband signal by the CDS circuit  2032 , the baseband signal is inputted to an A/D conversion circuit  2034 , converted to a digital signal, and inputted to a brightness detection circuit  2035 , which detects brightness (the average luminance of a signal). 
     A brightness signal detected by the brightness detection circuit  2035  is inputted to a light modulation circuit  2036 , and a modulated-light signal is generated for carrying out light modulation in accordance with the difference with a reference brightness (target value of modulated light). The modulated-light signal from the light modulation circuit  2036  is inputted to the diaphragm drive circuit  2023 , and the size of the opening of the diaphragm  2022  is adjusted so as to achieve the reference brightness. 
     A digital signal outputted from the A/D conversion circuit  2034  is inputted to a Y/C separation circuit  2037 , and a luminance signal Y and line-sequential color difference signals Cr (=2R−G) and Cb (=2B−G) (as broadly defined color signals C) are generated. The luminance signal Y is inputted to a selector  2039  via a γ circuit  2038  (the luminance signal is notated as Yh), and, in addition, is inputted to a first low-pass filter (abbreviated LPF)  2041 , which restricts the pass band of the signal. 
     The LPF  2041  is set to a broad pass band corresponding to the luminance signal Y, and a luminance signal Y 1  of the band set by the pass band characteristics of the LPF  2041  is inputted to a first matrix circuit  2042 . 
     Further, the color difference signals Cr, Cb are inputted to a (line-sequential) synchronization circuit  2044  via a second LPF  2043  for restricting the pass bands of the signals. 
     In this case, the second LPF  2043  changes the pass band characteristics thereof in accordance with the observation mode by the control circuit  2015 . More specifically, in the ordinary-light observation mode, the second LPF  2043  is set to a lower band than the first LPF  2041 . 
     Meanwhile, in the narrowband-light observation mode, the second LPF  2043  is changed to a broader band than the low band for the ordinary-light observation mode. For example, the second LPF  2043  is set (changed) to a broadband that is practically the same as that of the first LPF  2041 . Thus, the second LPF  2043  operates in response to the switching of the observation mode, forming processing characteristic changing means for changing the processing characteristics that restrict the pass band for the color difference signals Cr, Cb. 
     The synchronization circuit  2044  generates synchronized color difference signals Cr, Cb, and the color difference signals Cr, Cb are inputted to the first matrix circuit  2042 . 
     The first matrix circuit  2042  converts the luminance signal Y and color difference signals Cr, Cb to three primary color signals R, G, B, and outputs to the γ circuit  2045 . 
     Further, the first matrix circuit  2042  is controlled by the control circuit  2015 , and the value of matrix coefficients (determining the conversion characteristics) corresponding to the characteristics of the color separation filter  2030  of the CCD  2029 , or the characteristics of the narrowband filter  2024  is changed, and conversion to three primary color signals R 1 , G 1 , B 1 , which are not mixed colors or have had mixed colors eliminated for the most part, is performed. 
     For example, there are cases where the characteristics of the color separation filter  2030  of the CCD  2029  mounted in the endoscope  2002 , which is actually connected to the video processor  2004 , are different, and the control circuit  2015  changes the coefficients of the first matrix circuit  2042  in accordance with the characteristics of the color separation filter  2030  of the CCD  2029  that is actually being used according to the ID information, thus making it possible to appropriately deal with a situation in which the types of image-capturing means actually being used differ, making it possible to prevent the generation of pseudo-colors, and to convert to three primary color signals R 1 , G 1 , B  1  that are not mixed colors. 
     Furthermore, generating three primary color signals R 1 , G 1 , B 1 , which are not mixed colors, has the operational advantage of making it possible to effectively prevent a color signal, the image of which was captured under narrowband light of a specific color, from becoming difficult to be identified due to a color signal that was captured under a narrowband light of another color. 
     In other words, in the prior art shown in  FIG. 48 , the drawback is that a plurality of image components captured under respective narrowband lights respectively set in each of the wavelength bands of R, G, and B blend together to produce a mixed color, thereby obscuring the characteristic feature of an image component corresponding to a specific narrowband light of note, but the present embodiment makes it possible to prevent mixed colors that result in this kind of obscuring. 
     Further, preventing the mixing of colors can also make it possible in subsequent stages to produce a display by increasing the ratio of a noteworthy image component corresponding to a specific narrowband light, and to produce a display using only a noteworthy image component corresponding to a specific narrowband light, thereby also making it possible to produce an image display that clearly reflects the characteristic features of a noteworthy image component corresponding to a specific narrowband light. 
     The γ circuit  2045  is also controlled by the control circuit  2015 . Specifically, in the narrowband-light observation mode, the control circuit  2015  changes a γ correction characteristic to a γ characteristic that is highlighted more than in the ordinary-light observation mode. Thus, the contrast at the low signal level side is highlighted, making for display characteristics that are easier to identify. Three primary color signals R 2 , G 2 , B 2 , which have undergone γ correction by the γ circuit  2045 , are inputted to the second matrix circuit  2046 , and the second matrix circuit  2046  converts the three primary color signals R 2 , G 2 , B 2  to a luminance signal Y and color difference signals R-Y, B-Y. 
     In this case, the control circuit  2015  sets matrix coefficients of the second matrix circuit  2046  so as to simply convert the three primary color signals R 2 , G 2 , B 2  to a luminance signal Y and color difference signals R-Y, B-Y in the ordinary-light observation mode. 
     In the narrowband-light observation mode, the control circuit  2015  changes matrix coefficients of the second matrix circuit  2046  from the value of the ordinary-light observation mode, setting this value such that a luminance signal Ynbi, which increases the ratio (weight) for the B signal in particular, and color difference signals R-Y, B-Y are generated from the three primary color signals R 2 , G 2 , B 2 . 
     The conversion equation in this case is as follows when using three-row, three-column matrices A and K. 
     
       
         
           
             
               
                 
                   
                     ( 
                     
                       
                         
                           Ynbi 
                         
                       
                       
                         
                           
                             R 
                             - 
                             Y 
                           
                         
                       
                       
                         
                           
                             B 
                             - 
                             Y 
                           
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       A 
                       ⁡ 
                       
                         ( 
                         
                           
                             
                               0 
                             
                             
                               
                                 k 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             
                               0 
                             
                           
                           
                             
                               0 
                             
                             
                               0 
                             
                             
                               
                                 k 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                               
                             
                           
                           
                             
                               0 
                             
                             
                               0 
                             
                             
                               
                                 k 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 3 
                               
                             
                           
                         
                         ) 
                       
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           
                             
                               R 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                           
                         
                         
                           
                             
                               G 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                           
                         
                         
                           
                             
                               B 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     Here, matrix K, for example, comprises three real components k1 through k3 (the other component is 0), and, a conversion equation like Equation (4) increases the weight of G and B color signals relative to the R color signal, and maximizes the weight (ratio) of the color signal of B in particular. In other words, equation (4) suppresses the long-wavelength R color signal, and highlights the short-wavelength B color signal. 
     Further, A is a matrix for converting from an RGB signal to Y and color difference signals, and the following known operation coefficients (5) can be used. 
     
       
         
           
             
               
                 
                   A 
                   = 
                   
                     ( 
                     
                       
                         
                           0.299 
                         
                         
                           0.587 
                         
                         
                           0.114 
                         
                       
                       
                         
                           
                             - 
                             0.299 
                           
                         
                         
                           
                             - 
                             0.587 
                           
                         
                         
                           0.886 
                         
                       
                       
                         
                           0.701 
                         
                         
                           
                             - 
                             0.587 
                           
                         
                         
                           
                             - 
                             0.114 
                           
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     The luminance signal Ynbi outputted by the second matrix circuit  2046  is inputted to the selector circuit  2039 . The switching of the selector  2039  is controlled by the control circuit  2015 . That is, the control circuit  2015  selects luminance signal Yh in the ordinary-light observation mode, and selects luminance signal Ynbi in the narrowband-light observation mode. 
     The color difference signals R-Y, B-Y outputted from the second matrix circuit  2046  are inputted to an enlargement circuit  2047  together with either a Yh or Ynbi (notated as Yh/Ynbi) luminance signal that has passed through the selector  2039 . 
     A luminance signal Yh/Ynbi, which has undergone enlargement processing by the enlargement circuit  2047 , is inputted to a third matrix circuit  2049  subsequent to undergoing contour highlighting by a highlighting circuit  2048 , and the color difference signals R-Y, B-Y, which underwent enlargement processing by the enlargement circuit  2047 , are inputted to the third matrix circuit  2049  without passing through the highlighting circuit  2048 . 
     Then, the luminance signal Yh/Ynbi and color difference signals R-Y, B-Y are converted to three primary color signals R, G, and B by the third matrix circuit  2049 , and thereafter, the three primary color signals R, G, B are converted to analog video signals by a D/A conversion circuit not shown in the figure, and outputted to the monitor  2005  from a video signal output terminal. 
     Furthermore, the contour highlighting by the highlighting circuit  2048  may have highlighting characteristics changed corresponding to CCD  2029  and type of color separation filter  2030  and the like (the highlighting band can be changed to a medium/low band, or it can be changed to a medium/high band). 
     In particular, the luminance signal Ynbi is subjected to highlight processing in the narrowband-light observation mode. In this case, when equation (5) is employed, processing is carried out for highlighting the structure of capillary vessels and the like in the vicinity of the superficial portion of a living tissue via the B signal as will be explained below, making it possible to clearly display a noteworthy image component. 
     Furthermore, the three primary color signals R, G, B, which are actually inputted to the respective R, G, B channels of the monitor  5  from the video signal output terminal, constitute G, B, B signals (weighting differs according to the coefficients) when equation (5) is employed in the narrowband-light observation mode, and more particularly, the ratio of the B signal becomes the largest, making it possible to display in an easy-to-identify state via a B signal an endoscopic image corresponding to the structure of a capillary vessel in the vicinity of a superficial portion of a living tissue. 
     In other words, the signals respectively inputted to the RGB channels of the monitor  5  in the narrowband-light observation mode actually constitute G, B, B signals (apart from the value of the coefficients). 
     Thus, a feature of the present embodiment is the formation of processing characteristic changing means for changing a processing characteristic of a signal processing system of the video processor  2004  (more specifically, a signal processing system other than the Y/C separation circuit  2037 ) so as to be able to carry out signal processing that is suited to the respective observation modes by operating in response to the switching of the observation modes. 
     In this case, a characteristic feature is that it is possible to carry out processing that is suitable to both observation modes by changing the processing characteristics in practically compatible processing circuits without providing a dedicated processing circuit for each observation mode, enabling both observation modes to be appropriately supported using a simple configuration. 
     Operations according to the present embodiment will be explained hereinbelow by referring to  FIG. 43 . 
     An operator connects an endoscope  2002  to the light-source apparatus  2003  and video processor  2004  as shown in  FIG. 40 , and turns on the power, and the control circuit  2015  of the video processor  2004  starts initialization processing, and as shown in Step S 21 , for example, sets the ordinary-light observation mode as the operation mode of the light-source apparatus  2003  and video processor  2004 . 
     In this state, the light-source apparatus  2003  is set such that the narrowband filter  2024  is separated from the illumination light path as indicated by the solid line in  FIG. 40 , constituting a state in which image capturing is performed by the endoscope  2002  under white illumination light. Further, the respective parts of the video processor  2004  are also set to perform signal processing in the state of the ordinary-light observation mode. 
     An operator inserts the insertion unit  2007  of the endoscope  2002  into a body cavity of a patient, making it possible to conduct an endoscopic examination. When he wants to observe in more detail the course of the surface blood vessels of a tissue targeted for examination, such as a diseased part of the body cavity, the operator operates the mode-switching switch  2014 . 
     As shown in step S 22 , the control circuit  2015  monitors whether or not the mode-switching switch  2014  has been operated, and when the mode-switching switch  2014  has not been operated, it maintains the status, and when the mode-switching switch  2014  has been operated, it proceeds to the next step S 23 . 
     In step S 23 , the control circuit  2015  changes the operation mode of the light-source apparatus  2003  and video processor  2004  to the setting state of the narrowband-light observation mode. 
     More specifically, the control circuit  2015  performs control relative to the light-source apparatus  2003  such that the narrowband filter  2024  is positioned in the illumination light path as indicated by the two-dot chain line in  FIG. 40 . As indicated by the transmittance characteristics shown in  FIG. 41 , positioning the narrowband filter  2024  in the path of the illumination light results in illumination by a narrowband illumination light in accordance with the narrowband transmission filter characteristic sections Ra, Ga, Ba. 
     Further, the control circuit  2015  changes the settings of the respective parts of the video processor  2004 . More specifically, the control circuit  2015  carries out changes and settings so as to make the band characteristics of the LPF  2043  broadband, change the matrix coefficients of the first matrix circuit  2042  such that a mixed color is not generated, change a γ characteristics of the γ circuit  2045 , change the matrix coefficients of the second matrix circuit  2046  so as to increase the ratio of the signal component of a B color signal (according to the narrowband transmission filter characteristic section Ba) in particular, and switch the selector  2039  such that luminance signal Ynbi is selected. 
     By making changes and settings like this, the matrix coefficients of the second matrix circuit  2046 , for example, are changed to processing characteristics, which increase the ratio of the signal components of a B color signal in particular, thereby making it possible to display in an easy-to-identify state the course of a capillary vessel in the vicinity of a superficial portion of a living tissue achieved by a B color signal, the image of which was captured under B illumination light via the narrowband transmission filter characteristic section Ba. 
     Further, since the band characteristics of the signal pass-band of LPF  2043  are made broadband, it is possible to enhance the resolution (resolving power) of the course of a capillary vessel, and the course of a blood vessel in the vicinity of a superficial portion achieved by a G color signal, the image of which was captured under G illumination light approaching the luminance signal via the narrowband transmission filter characteristic section Ga. 
     In the next step S 24 , the control circuit  2015  monitors whether or not the mode-switching switch  2014  has been operated, and when the mode-switching switch  2014  has not been operated, maintains the status, and when the mode-switching switch  2014  has been operated, returns to the next step S 21 . 
     According to the present embodiment, which operates like this, retaining a color image-capturing function in accordance with an existing synchronous system and changing processing characteristics, such as changing the coefficients and other settings of the respective parts of the video processor  2004 , in the ordinary-light observation mode, makes it possible to ensure full observation functions in the narrowband-light observation mode. 
     That is, in the prior art, preventing a drop in resolving power makes it possible to achieve an endoscopic image having good resolution, and to more clearly display in an easy-to-identify state the course of a capillary vessel, the image of which was captured under a B narrowband illumination light (which, for example, was apt to be buried in the prior art due to the signal having its image captured under R narrowband illumination light). 
     Further, according to the present embodiment, it is possible to readily support both the ordinary-light observation mode and the narrowband-light observation mode by switching the processing characteristics of a portion of the signal processing system, thereby achieving an apparatus that is extremely convenient and useful during an endoscopic examination. 
     Further, a light-source apparatus of a narrowband light can be readily formed by providing in the light-source apparatus  2003  means for removably inserting a narrowband filter  2024  in the optical path, in addition to ordinary-light illumination means. 
     A first variation of the fourth embodiment will be explained next. In the fourth embodiment, multiplication processing is reduced by using a first matrix circuit  2042  to carry out processing as below. 
     The above-mentioned first matrix circuit  2042  generates three primary color signals R 1 , G 1 , B 1  from an inputted luminance signal Y and color difference signals Cr, Cb. 
     In this case, the matrix operation equation by the first matrix circuit  2042  uses a three-row, three-column matrix M (matrix coefficients m11 through m33), and generally is as follows. 
     
       
         
           
             
               
                 
                   
                     ( 
                     
                       
                         
                           
                             R 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                       
                       
                         
                           
                             G 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                       
                       
                         
                           
                             B 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               11 
                             
                           
                           
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               12 
                             
                           
                           
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               13 
                             
                           
                         
                         
                           
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               21 
                             
                           
                           
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               22 
                             
                           
                           
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               23 
                             
                           
                         
                         
                           
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               31 
                             
                           
                           
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               32 
                             
                           
                           
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               33 
                             
                           
                         
                       
                       ) 
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           
                             Y 
                           
                         
                         
                           
                             Cr 
                           
                         
                         
                           
                             Cb 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     Meanwhile, the luminance signal Y and color difference signals Cr, Cb inputted to the first matrix circuit  2042  have the characteristics generally depicted in  FIG. 44 . 
     If the ratios (percentages) of the contributions of luminance signal Y and color difference signals Cr and Cb relative to the respective bands of R, G, and B in  FIG. 44  are taken into account when carrying out the operation of the above equation (6), the following approximations can be made. The ratio contributed by color difference signal Cb in the R band in  FIG. 44  can be approximated as 0, which is sufficiently smaller than those of the others. 
     That is, the above-mentioned coefficient m 13  can be approximated as 0. Further, the ratio contributed by color difference signal Cr in the G band can be approximated as a sufficiently small 0. That is, the above-mentioned coefficient m 22  can be approximated as 0. 
     Further, the ratio contributed by color difference signal Cr in the B band can be approximated as a sufficiently small 0. That is, the above-mentioned coefficient m 32  can be approximated as 0. 
     Therefore, the following equation can be employed as the above-mentioned matrix M. 
     
       
         
           
             
               
                 
                   M 
                   = 
                   
                     ( 
                     
                       
                         
                           
                             m 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             11 
                           
                         
                         
                           
                             m 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             12 
                           
                         
                         
                           0 
                         
                       
                       
                         
                           
                             m 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             21 
                           
                         
                         
                           0 
                         
                         
                           
                             m 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             23 
                           
                         
                       
                       
                         
                           
                             m 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             31 
                           
                         
                         
                           0 
                         
                         
                           
                             m 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             33 
                           
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     The coefficients of the matrix M are shown in  FIG. 45(A) . Further, the coefficients of the matrix M can also be approximated from the characteristics of  FIG. 44  as in  FIG. 45(B) ,  FIG. 45(C) , and  FIG. 45(D) . By approximating like this, it becomes possible to reduce or simplify the configuration of the multiplier of the first matrix circuit  2042 , enabling high-speed processing and lower costs. 
     Next, a second variation of the fourth embodiment will be explained. In the above explanation, the narrowband filter  2024  employed a three-peak filter, but a two-peak filter such as that below can also be used. 
     A filter with transmittance characteristics like those shown in  FIG. 46  can be employed as the narrowband filter  2024 B in the second variation. The narrowband filter  2024 B is a two-peak filter, and it has the respective narrowband transmission filter characteristic sections Ga and Ba in the G and B wavelength regions. That is, this filter does not provide the narrowband transmission filter characteristic section Ra of the three-peak narrowband filter  2024  in the fourth embodiment. 
     More specifically, the narrowband transmission filter characteristic sections Ga, Ba have bandpass characteristics in which the center wavelengths are 420 nm and 540 nm, respectively, and the full widths at half maximum are between 20 nm and 40 nm. 
     Therefore, when the narrowband filter  2024 B is positioned in the illumination light path, the two-band narrowband illumination light, which permeates the narrowband transmission filter characteristic sections Ga, Ba thereof is irradiated into the light guide  2013 . 
     The matrix operation equation of the first matrix circuit  2042  in this case uses a two-row, three-column matrix M, and generally is as follows. 
     
       
         
           
             
               
                 
                   
                     ( 
                     
                       
                         
                           
                             G 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                       
                       
                         
                           
                             B 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               21 
                             
                           
                           
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               22 
                             
                           
                           
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               23 
                             
                           
                         
                         
                           
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               31 
                             
                           
                           
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               32 
                             
                           
                           
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               33 
                             
                           
                         
                       
                       ) 
                     
                     * 
                     
                       ( 
                       
                         
                           
                             Y 
                           
                         
                         
                           
                             Cr 
                           
                         
                         
                           
                             Cb 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     Meanwhile, the luminance signal Y and color difference signals Cr, Cb inputted to the first matrix circuit  2042  have the characteristics depicted in  FIG. 44 . Then, carrying out approximation the same way as expressed in equation (7) makes it possible to approximate the coefficients m22 and m32 as 0. 
     That is, in this case, the equation becomes as follows. 
                   M   =     (           m   ⁢           ⁢   21         0         m   ⁢           ⁢   23               m   ⁢           ⁢   31         0         m   ⁢           ⁢   33           )             (   9   )               
This is depicted in  FIG. 47(A) . Further, carrying out approximation via another method makes it possible to use a coefficient matrix M such as coefficients of  FIG. 47(B)  and  FIG. 47(C) .
 
     Approximating a portion of the coefficients of the matrix M as 0 like this makes it possible to reduce the number of multipliers. Further, it also has the effect of enabling matrix computations to be processed faster. In addition, using a two-peak filter also makes it possible to lower the cost of an expensive narrowband filter. 
     Fifth Embodiment 
     Next, a fifth embodiment of the present invention will be explained by referring to  FIG. 49 .  FIG. 49  shows an endoscope apparatus  2001 B according to the fifth embodiment of the present invention. Since the fifth embodiment is practically the same as the fourth embodiment, only the points of difference will be explained, and an explanation of identical components having the same reference numerals will be omitted. 
     The endoscope apparatus  2001 B employs a video processor  2004 B that changes a portion of the video processor  2004  of  FIG. 40 . The video processor  2004 B configures the first matrix circuit  2042 , γ circuit  2045 , and second matrix circuit  2046  in the video processor  2004  of  FIG. 40  into a single matrix circuit  2051 . 
     Then, the control circuit  2015  changes the matrix coefficients of the matrix circuit  2051  the same as it changed a γ characteristic of the γ circuit  2045  and the matrix coefficients of the second matrix circuit  2046  by switching signals via the mode-switching switch  2014  as explained in the fourth embodiment. 
     When the observation mode is switched from the ordinary-light observation mode to the narrowband-light observation mode, processing for performing a conversion without mixed colors, for changing a γ characteristic, and for performing a conversion, which suppresses a long-wavelength color signal (highlights a short-wavelength color signal) is collectively carried out by changing the coefficients of the matrix circuit  2051 . 
     Further, an AGC circuit  2052 , which applies auto-gain control to the signal level of input signals, is provided between the A/D conversion circuit  2034  and the Y/C separation circuit  2037 . 
     Further, the configuration is such that an output signal of the CDS circuit  2032 , and a luminance signal Ynbi from the matrix circuit  2051  are inputted to the brightness detection circuit  2035 . Also, the control circuit  2015  changes the AGC gain and the follow-up speed of the AGC circuit  2052  in accordance with the observation mode by switching the mode-switching switch  2014 . 
     Specifically, in the narrowband-light observation mode, the control circuit  2015  sets the AGC gain of the AGC circuit  2052  higher than it was in the ordinary-light observation mode, and, for example, also sets the follow-up speed of AGC gain control slower than the diaphragm control speed of the diaphragm  2022  of the light-source apparatus  2003 . This gives priority to the light modulation operation of the diaphragm  2022  over the signal gain control operation of the AGC circuit  2052 . 
     Further, the control circuit  2015  also switches the reference brightness (target light modulation value) in the light modulation circuit  2036  in the ordinary-light observation mode and in the narrowband-light observation mode. 
     By doing thus, light modulation is carried out giving priority to the light modulation operation of the diaphragm  2022  in the light-source apparatus  2003 . When light modulation cannot be adequately performed by the diaphragm  2022  in accordance with this light modulation operation, an auto-gain control operation is supplementary carried out by the AGC circuit  2052 . 
     Specifically, since the AGC circuit  2052  is designed to function when the diaphragm  2022  is open and the quantity of illumination light is at the maximum but the brightness is still not sufficient, (prior to the diaphragm  2022  opening) the AGC circuit  2052  operates, making it possible to prevent S/N degradation, and to achieve an endoscopic image of appropriate brightness. 
     According to the present embodiment, the configuration is such that, in addition to the operational advantages of the fourth embodiment, it is also possible to prevent S/N degradation, and to achieve an endoscopic image of appropriate brightness, particularly in the narrowband-light observation mode. 
     Sixth Embodiment 
       FIGS. 50 through 68  are related to a sixth embodiment of the present invention.  FIG. 50  is an external view showing the external configuration of an endoscope apparatus;  FIG. 51  is a diagram showing the front panel of the light-source apparatus of  FIG. 50 ;  FIG. 52  is a diagram showing the front panel of the video processor of  FIG. 50 ;  FIG. 53  is block diagram showing a configuration of the endoscope apparatus of  FIG. 50 ;  FIG. 54  is a block diagram showing a configuration of the rotating filters of  FIG. 53 ;  FIG. 55  is a diagram showing the spectral characteristics of a first filter group of the rotating filter of  FIG. 54 ;  FIG. 56  is a diagram showing the spectral characteristics of a second filter group of the rotating filter of  FIG. 54 ;  FIG. 57  is a diagram showing the layered structure of a living tissue observed via the endoscope apparatus of  FIG. 53 ;  FIG. 58  is a diagram illustrating the access state in the direction of the layers of a living tissue of illumination light from the endoscope apparatus of  FIG. 53 ;  FIG. 59  is a first diagram showing the respective band images resulting from the surface-sequential light permeating the first filter group of  FIG. 55 ;  FIG. 60  is a second diagram showing the respective band images resulting from the surface-sequential light permeating the first filter group of  FIG. 55 ;  FIG. 61  is a third diagram showing the respective band images resulting from the surface-sequential light permeating the first filter group of  FIG. 55 ;  FIG. 62  is a first diagram showing the respective band images resulting from the surface-sequential light permeating the second filter group of  FIG. 56 ;  FIG. 63  is a second diagram showing the respective band images resulting from the surface-sequential light permeating the second filter group of  FIG. 56 ;  FIG. 64  is a block diagram showing a configuration of the white balance circuit of  FIG. 53 ;  FIG. 65  is an external view showing the external configuration of a first variation of the endoscope apparatus of  FIG. 50 ;  FIG. 66  is an external view showing the external configuration of a second variation of the endoscope apparatus of  FIG. 50 ;  FIG. 67  is a block diagram showing a configuration of a synchronous-type endoscope apparatus, which is a variation of the endoscope apparatus of  FIG. 53 ; and  FIG. 68  is a block diagram showing a configuration of the white balance circuit of  FIG. 67 . 
     In ordinary-light observation, white balance is achieved in order to compensate for the irregularities of the various optical characteristics. In white balance, a correction value for multiplying a R signal and a B signal is obtained, and RGB signals output at white-light observation are made uniform. This makes it possible to suppress the affect of the above-mentioned irregularities on color reproducibility. 
     White balance must also be achieved prior to the start of an examination in narrowband-light observation (NBI observation) the same as in ordinary-light observation. This makes it possible to correct the irregularities of an optical filter for narrowband light, and stabilizes color reproducibility. 
     The illumination light in narrowband-light observation (NBI observation) used to be three-band R, G, B narrowband light, but the problem of changing to the two bands of G and B narrowband light in order to stabilize the reproducibility of mucous membrane information using narrowband light is that an R-light-based video signal cannot be achieved with a surface-sequential-type narrowband light, and therefore, since a G signal output is divided by an R signal output for a white balance correction value the same as with ordinary light, it becomes impossible to calculate the correction value for an R signal. Further, with synchronous-type narrowband light as well, it is impossible to employ the same correction value calculation method as with ordinary light because two signals are produced by converting from YCrCb, and the two signals do not include an R signal. 
     With the foregoing in view, it is an object of the present embodiment and a seventh embodiment, which will be explained hereinbelow, to provide an endoscope apparatus, which makes it possible to switch to white balance that corresponds to ordinary-light observation and narrowband-light observation. 
     As shown in  FIG. 50 , an endoscope apparatus  3001  of the present embodiment includes an electronic endoscope  3003  including a CCD  3002 , which will be explained hereinbelow as image-capturing means, which is inserted into a body cavity, and which captures an image of body cavity tissue; a light-source apparatus  3004 , which supplies illumination light to the electronic endoscope  3003 ; and a video processor  3007 , which carries out signal processing of an image-capturing signal from the CCD  3002  of the electronic endoscope  3003 , and displays an endoscopic image on an observation monitor  3005 . 
     Front panels  3004   a  and  3007   a  are disposed on the front of the light-source apparatus  3004  and the video processor  3007 , and, as shown in  FIG. 51 , a narrowband light observation mode display unit  3004   b  for notifying that the endoscope apparatus  3001  is in the narrowband-light observation mode is provided on the front panel  3004   a  of the light-source apparatus  3004 . Further, a white balance switch  3007   c , which indicates acquisition of white balance of an image-capturing signal from the CCD  3002 , and a narrowband-light observation mode display unit  7300   b  for notifying that the endoscope apparatus  3001  is in the narrowband-light observation mode are provided on the front panel  3007   a  of the video processor  3007  as shown in  FIG. 52 . 
     In an endoscopic examination with the electronic endoscope  3003 , which utilizes the light-source apparatus  3004  and video processor  3007 , white balance must be achieved prior to examination, but in this case, white balance processing is performed by attaching a tubular white cap  3045 , the inside of which has been made white, to the distal end of an insertion unit  3003   a  of the electronic endoscope  3003 . 
     Meanwhile, when performing an examination using a special observation light, such as a narrowband light, white balance processing must be performed a total of two times, once each for an ordinary light and a special light. 
     However, since white balance processing is performed one time when conducting an ordinary endoscopic examination using ordinary light, there is the risk that the white cap  3045  may be removed from the end of the insertion unit  3003   a  of the electronic endoscope  3003  prior to the second white balance processing being completed, making it impossible to carry out the second white balance processing normally. 
     Accordingly, in the present embodiment, by notifying of the narrowband-light observation mode via the narrowband-light observation mode display units  3004   b ,  3007   b  provided on the front panels  3004   a ,  3007   a , the fact that white balance processing of the narrowband light is in progress is visually recognizable from the narrowband-light observation mode display units  3004   b ,  3007   b.    
     As shown in  FIG. 53 , the video processor  3007  is constituted so as to enable an endoscopic image to be encoded and outputted to an image filing apparatus  3006  as a compressed image. 
     The light-source apparatus  3004  includes a xenon lamp  3011  for emitting illumination light; a heat cutting filter  3012  for blocking the heat of a white light; a diaphragm device  3013  for controlling the quantity of light of a white light via the heat cutting filter  3012 ; a rotating filter  3014  for making the illumination light a surface-sequential light; a condensing lens  3016  for condensing the surface-sequential light via the rotating filter  3014  on the incident surface of a light guide  3015  arranged inside the electronic endoscope  3003 ; and a control circuit  3017  for controlling the rotation of the rotating filter  3014 . 
     The rotating filter  3014 , as shown in  FIG. 54 , is constituted in a disk shape, and has a dual structure centered around an axis of rotation, an R 1  filter section  3014   r   1 , a G 1  filter section  3014   g   1 , and a B 1  filter section  3014   b   1 , which constitute a first filter group for outputting surface-sequential light of overlapping spectral characteristics, which, as shown in  FIG. 55 , is well suited to color reproduction, are arranged in the outer radial part, and a G 2  filter section  3014   g   2 , a B 2  filter section  3014   b   2 , and a shading filter section  3014 Cut, which constitute a second filter group for outputting narrowband surface-sequential light of discrete spectral characteristics, capable, as shown in  FIG. 56 , of extracting the desired layer tissue information, are arranged in the inner radial part. 
     Then, as shown in  FIG. 53 , the rotating filter  3014  is rotated in accordance with the control circuit  3017  driving and controlling a rotating filter motor  3018 , and movement in the radial direction (movement, which is perpendicular to the optical path of the rotating filter  3014 , and which selectively moves the first filter group and second filter group of the rotating filter  3014  in the optical path) is carried out by a mode switching motor  3019  in accordance with a control signal from a mode switching circuit  3042  inside the video processor  3007 , which will be explained hereinbelow. 
     Furthermore, power is supplied from a power unit  3010  to the xenon lamp  3011 , diaphragm device  3013 , rotating filter motor  3018 , and mode switching motor  3019 . 
     The video processor  3007  includes a CCD drive circuit  3020  for driving the CCD  3002 ; an amplifier  3022  for amplifying an image-capturing signal, which is an image of a body cavity tissue captured by the CCD  3002  via an objective optical system  3021 ; a processing circuit  3023 , which performs correlated double sampling and noise removal for an image-capturing signal through the amplifier  3022 ; an A/D converter  3024  for converting an image-capturing signal that has passed through the processing circuit  3023  to digital signal image data; a white balance circuit (W.B.)  3025  for performing white balance processing on the image data from the A/D converter  3024 ; a selector  3026  and synchronization memories  3027 ,  3028 ,  3029  for synchronizing surface-sequential light using the rotating filter  3014 ; an image processing circuit  3030  for reading out the respective image data of the surface-sequential light stored in the synchronization memories  3027 ,  3028 ,  3029 , and performing gamma correction processing, contour highlight processing, and color processing; D/A circuits  3031 ,  3032 ,  3033  for converting image data from the image processing circuit  3030  to analog signals; an encoding circuit  3034  for encoding image data from the image processing circuit  3030 ; and a timing generator (T.G.)  3035  for inputting from the control circuit  3017  of the light-source apparatus  3004  a synchronization signal synchronized to the rotation of the rotating filter  3014 , and outputting various timing signals to the above-described respective circuits. 
     Further, a mode-switching switch  3041  is provided in the electronic endoscope  3002 , and the output of the mode-switching switch  3041  is outputted to a mode-switching circuit  3042  inside the video processor  3007 . The mode-switching circuit  3042  of the video processor  3007  outputs control signals to the white balance circuit (W.B.)  3025 , a light modulation circuit  3043 , a light modulation control parameter switching circuit  3044 , and the mode-switching motor  3019  of the light-source apparatus  3004 . The light modulation control parameter switching circuit  3044  outputs a light modulation control parameter corresponding to the first filter group and the second filter group of the rotating filter  3014  to the light modulation circuit  3043 , and the light modulation circuit  3043  performs proper brightness control by controlling the diaphragm device  3013  of the light-source apparatus  3004  based on the control signal from the mode-switching circuit  3042  and the light modulation control parameter from the light modulation control parameter switching circuit  3044 . 
     As shown in  FIG. 57 , in most cases, for example, body cavity tissue  3051  has an absorbent distributed structure of blood vessels and the like that differ in the depth direction. In the vicinity of the superficial portion of the mucous membrane, mainly capillary vessels  3052  are distributed in large numbers, and in the intermediate layer, which is deeper than the superficial layer, blood vessels  3053  that are larger than capillary vessels are distributed in addition to capillary vessels, and in yet a deeper layer, even larger blood vessels  3054  are distributed. 
     Meanwhile, the invasion depth in the depth direction of light relative to a body cavity tissue  3051  is dependent on the wavelength of the light, and when illumination light including the visible region is a short wavelength like that of blue (B), as shown in  FIG. 58 , the light only penetrates as far as the vicinity of the superficial layer as a result of the absorption characteristics and scattering characteristics of the living tissue, is subjected to absorption and scattering in that depth range, and the light that exits from the surface is observed. Further, in the case of green (G) light, which has a longer wavelength than blue (B) light, the light penetrates deeper than the range to which the blue (B) light penetrates, is subjected to absorption and scattering in that range, and the light that exits from the surface is observed. And red (R) light, which has a longer wavelength than green (G) light, reaches an even deeper range. 
     At ordinary observation, the mode switching circuit  3042  inside the video processor  3007  controls the mode switching motor  3019  via a control signal such that the R 1  filter  3014   r   1 , G 1  filter  3014   g   1 , and B 1  filter  3014   b   1 , which are the first filter group of the rotating filter  3014 , are located in the optical path of the illumination light. 
     As shown in  FIG. 55 , because the respective wavelength regions of the R 1  filter  3014   r   1 , G 1  filter  3014   g   1 , and B 1  filter  3014   b   1  overlap one another at ordinary observation of a body cavity tissue  3051 , (1) a band image including shallow layer and intermediate layer tissue information, which includes numerous tissue information of the shallow layer as shown in  FIG. 59 , is captured in an image-capturing signal, which is an image captured by the CCD  3004  via the B 1  filter section  3014   b   1 ; (2) further, a band image including shallow layer and intermediate layer tissue information, which includes numerous tissue information of the intermediate layer as shown in  FIG. 60 , is captured in an image-capturing signal, which is an image captured by the CCD  3004  via the G 1  filter section  3014   g   1 ; and (3) in addition, a band image including intermediate layer and deep layer tissue information, which includes numerous tissue information of the deep layer as shown in  FIG. 61 , is captured in an image-capturing signal, which is an image captured by the CCD  3004  via the R 1  filter section  3014   r   1 . 
     Then, an endoscopic image of a desired or natural color reproduction can be obtained as the endoscopic image by the video processor  3007  synchronizing the RGB image-capturing signals and performing signal processing. 
     Meanwhile, if the mode-switching switch  3041  of the electronic endoscope  3003  is pressed, the signal is inputted to the mode switching circuit  3042  of the video processor  3007 . By outputting a control signal to the mode switching motor  3019  of the light-source apparatus  3004 , the mode switching circuit  3042  drives the rotating filter  3014  relative to the optical path so as to move the first filter group of the rotating filter  3014 , which was in the optical path at ordinary observation, and position the second filter group in the optical path. 
     As shown in  FIG. 56 , because the G 2  filter section  3014   g   2 , B 2  filter section  3014   b   2 , and shading filter section  3014 Cut change the illumination light to narrowband surface-sequential light of discrete spectral characteristics, and their respective wavelength regions do not overlap when body cavity tissue  3051  is being observed under narrowband light using the second filter group, (4) a band image including tissue information of the shallow layer as shown in  FIG. 62  is captured in an image-capturing signal, which is an image captured by the CCD  3004  via the B 2  filter section  3014   b   2 ; and (5) a band image including tissue information of the intermediate layer as shown in  FIG. 63  is captured in an image-capturing signal, which is an image captured by the CCD  3004  via the G 2  filter section  3014   g   2 . 
     Meanwhile, the white balance circuit  3025  includes a white balance correction unit  3080 , and a white balance correction value calculation unit  3081 , as shown in  FIG. 64 . 
     In the endoscope apparatus  3001  of the present embodiment, white balance is achieved prior to an examination by attaching a tubular white cap  3045 , the inside of which has been made white, to the distal end of the insertion unit  3003   a  of the electronic endoscope  3003 . 
     Specifically, when the white balance switch  3007 C provided on the front panel  3007   a  of the video processor  3007  is pressed in a state in which the white cap  3045  is attached to the distal end of the insertion unit  3003   a  of the electronic endoscope  3003 , the first filter group of the rotating filter  3014  in the light-source apparatus  3003  is positioned in the optical path, and white balance is achieved a first time for ordinary light by the white balance circuit  3025  of the video processor  3007 . Then, once white balance has been achieved at ordinary light, the second filter group of the rotating filter  3014  in the light-source apparatus  3003  is positioned in the optical path, and white balance is achieved by the white balance circuit  3025  of the video processor  3007  a second time for narrowband light. While white balance is being achieved a first time and second time, the narrowband-light observation mode display unit  3004   b  provided on the front panel  3004   a  of the light-source apparatus  3003 , and the narrowband-light observation mode display unit  3007   b  provided on the front panel  3007   a  of the video processor  3007  are lit up in a prescribed color. 
     Furthermore, the color that lights while white balance is being achieved the first time, and the color that lights while white balance is being achieved the second time can be different colors. For example, the color that lights while white balance is being achieved the first time can be green, and the color that lights while white balance is being achieved the second time can be white. 
     In the white balance circuit  3025 , the white balance correction value calculation unit  3081  switches to the white balance correction value calculation method in accordance with a mode detection signal, which is a control signal from the mode-switching circuit  3042 . 
     Specifically, the first-time white balance for ordinary light is: 
     (R correction value)=(G average value)/(R average value), (B correction value)=(G average value)/(B average value) 
     Second-time white balance for narrowband light is: 
     (R correction value)=(prescribed fixed value), (B correction value)=(G average value)/(B average value) 
     Then, the white balance correction unit  3080  outputs a correction value for each signal by multiplying by the corresponding input signal. 
     Thus, in the present embodiment, since the white balance method is switched for ordinary light and narrowband light, a state in which it is impossible to calculate the correction value of an R signal can be avoided even when there are two bands of illumination light resulting from narrowband light, making white balance achievable. Further, the fact that a white balance operation is being carried out can be clearly understood visually, and using different colors makes it possible to visually glean which white balance operation is current being carried out. 
     Furthermore, in the present embodiment, it is supposed that white balance processing is performed in accordance with lighting up the narrowband-light observation mode display units  3004   b ,  3007   b  but the present invention is not limited to this, and as shown in  FIG. 65 , speakers  3061  and  3062  can be provided inside the light-source apparatus  3003  and the video processor  3007  so as to notify of white balance processing by sound. In this case, notification can be provided using the same sound while white balance is achieved a first time and a second time, or the sound generated while achieving white balance the first time can differ from the sound generated while achieving white balance the second time. The fact that a white balance operation is being carried out can be recognized as a sound, and which white balance operation is currently being performed can be gleaned without looking at the apparatus. 
     Further, as shown in  FIG. 66 , the configuration can be such that a message window  3063  is displayed on the observation monitor  3005 , and a message, such as, for example, “white balance in progress” is displayed in the message window  3063 . Notification can be provided using the same message, for example, “white balance in progress”, while white balance is achieved a first time and a second time, or the displayed message can be changed, such that the message displayed while achieving white balance the first time reads, for example, “white balance  1  in progress”, and the message displayed while achieving white balance the second time reads, for example, “white balance  2  in progress”. Furthermore, a message such as “white balance in progress” can be displayed during the achievement of white balance, and a message, such as “white balance not in progress” can be displayed when white balance is not being achieved. Displaying the fact that a white balance operation is being carried out on the observation monitor  3005  as character information further facilitates visual recognition. 
     Furthermore, in the endoscope apparatus  3001  of the above-described embodiments, the explanation used as an example a surface-sequential-type endoscope apparatus in which the light-source apparatus  3004  supplies surface-sequential light, and the video processor  3007  produces an image by synchronizing surface-sequential image information, however, the present invention is not limited to this, and a synchronous-type endoscope apparatus is also applicable. 
     That is, as shown in  FIG. 67 , a synchronous-type endoscope apparatus  3001 , which comprises a light-source apparatus  4  for supplying white light, an electronic endoscope  3003  including a color chip  3100  on the front face of the image-capturing surface of the CCD  3002 , and a video processor  3007 , which performs signal processing for image-capturing signals from the electronic endoscope  3003  can also apply the present embodiment. 
     In the light-source apparatus  3004 , white light from the xenon lamp  3011  passes through a heat cutting filter  3012 , the quantity of light is controlled by the diaphragm device  3013 , and the white light is outputted to the incident surface of the light guide  3015 , which is arranged inside the electronic endoscope  3003 . A narrowband interference filter  3014   a , which converts the white light to narrowband light of discrete spectral characteristics as shown in  FIG. 56 , is removably provided in the optical path. 
     In the electronic endoscope  3003 , an image of body cavity tissue  3051  is captured by the CCD  3002  through the color chip  3100 . 
     In the video processor  3007 , image data from the A/D converter  3024  is separated into a luminance signal Y and color difference signals Cr, Cb by the Y/C separation circuit  3101 , converted to RGB signals by the RGB matrix circuit  3102 , and outputted to the white balance circuit  3025 . The remaining configuration and operations are the same as those of the endoscope apparatus of  FIG. 53 . 
     Then, in the white balance circuit  3025 , as shown in  FIG. 68 , white balance is achieved for each signal of the RGB signals from the RGB matrix circuit  3102 . The white balance acquisition method at this time is the same as for the present embodiment. 
     Seventh Embodiment 
       FIG. 69  is a block diagram showing a configuration of a white balance circuit related to a seventh embodiment of the present invention. 
     Since the seventh embodiment is practically the same as the sixth embodiment, only the points of difference will be explained, and an explanation of identical components having the same reference numerals will be omitted. 
     In the surface-sequential-type endoscope apparatus  3001  shown in  FIG. 53 , the white balance circuit  3025  of the present embodiment includes an R/G/B signal generation unit  3082  like the one shown in  FIG. 69 , and the R/G/B signal generation unit  3082 , in response to the inputting of surface-sequential-type R/G/B signals, replaces the R signal in accordance with the observation mode, and thereafter, achieves white balance the same as the sixth embodiment. 
     That is, in the R/G/B signal generation unit  3082 , replacement is performed as follows: 
     Ordinary light: R signal←R signal 
     Narrowband light: R signal←G signal 
     The post-replacement signal is outputted to the white balance correction unit  3080 , and the white balance correction unit  3080  achieves white balance. 
     Furthermore, a B signal can be allocated to the R signal, and signal data prepared in advance can be used apart from the output of the CCD  3002 . 
     Eighth Embodiment 
       FIGS. 70 through 88  are related to an eighth embodiment of the present invention.  FIG. 70  is a block diagram showing a configuration of an endoscope apparatus;  FIG. 71  is a configuration diagram showing a configuration of the rotating filter of  FIG. 70 ;  FIG. 72  is a diagram showing the spectral characteristics of a first filter group of the rotating filter of  FIG. 71 ;  FIG. 73  is a diagram showing the spectral characteristics of a second filter group of the rotating filter of  FIG. 71 ;  FIG. 74  is a diagram showing the layered structure of a living tissue observed via the endoscope apparatus of  FIG. 70 ;  FIG. 75  is a diagram illustrating the access state in the direction of the layers of a living tissue of the illumination light from the endoscope apparatus of  FIG. 70 ;  FIG. 76  is a first diagram showing the respective band images resulting from the surface-sequential light permeating the first filter group of  FIG. 72 ;  FIG. 77  is a second diagram showing the respective band images resulting from the surface-sequential light permeating the first filter group of  FIG. 72 ;  FIG. 78  is a third diagram showing the respective band images resulting from the surface-sequential light permeating the first filter group of  FIG. 72 ;  FIG. 79  is a first diagram showing the respective band images resulting from the surface-sequential light permeating the second filter group of  FIG. 73 ;  FIG. 80  is a second diagram showing the respective band images resulting from the surface-sequential light permeating the second filter group of  FIG. 73 ;  FIG. 81  is a third diagram showing the respective band images resulting from the surface-sequential light permeating the second filter group of  FIG. 73 ;  FIG. 82  is a block diagram showing a configuration of the white balance circuit of  FIG. 70 ;  FIG. 83  is a block diagram showing a configuration of a variation of the white balance circuit of  FIG. 82 ;  FIG. 84  is a block diagram showing a configuration of a first variation of the endoscope apparatus of  FIG. 70 ;  FIG. 85  is a block diagram showing a configuration of the white balance circuit of  FIG. 84 ;  FIG. 86  is a block diagram showing a configuration of a second variation of the endoscope apparatus of  FIG. 70 ;  FIG. 87  is a block diagram showing a configuration of the white balance circuit of  FIG. 86 ; and  FIG. 88  is a block diagram showing a configuration of a variation of the white balance circuit of  FIG. 86 . 
     As shown in  FIG. 70 , an endoscope apparatus  4001  of the present embodiment includes an electronic endoscope  4003  including a CCD  4002  as image-capturing means, which is inserted into a body cavity, and which captures an image of the body cavity tissue; a light-source apparatus  4004 , which supplies illumination light to the electronic endoscope  4003 ; and a video processor  4007 , which performs signal processing of an image-capturing signal from the CCD  4002  of the electronic endoscope  4003 , and displays an endoscopic image on an observation monitor  4005 , and also encodes the endoscopic image and outputs as a compressed image to an image filing apparatus  4006 . 
     The light-source apparatus  4004  includes a xenon lamp  4011  for emitting illumination light; a heat cutting filter  4012  for blocking the heat of a white light; a diaphragm device  4013  for controlling the quantity of light of a white light via the heat cutting filter  4012 ; a rotating filter  4014  for making an illumination light into a surface-sequential light; a condensing lens  4016  for condensing the surface-sequential light via the rotating filter  4014  on the incident surface of a light guide  4015  arranged inside the electronic endoscope  4003 ; and a control circuit  4017  for controlling the rotation of the rotating filter  4014 . 
     The rotating filter  4014 , as shown in  FIG. 71 , is constituted in a disk shape, and has a dual structure centered around an axis of rotation, an R 1  filter section  4014   r   1 , a G 1  filter section  4014   g   1 , and a B 1  filter section  4014   b   1 , which constitute a first filter group for outputting surface-sequential light of overlapping spectral characteristics, which, as shown in  FIG. 72 , is well suited to color reproduction, are arranged in the outer radial part, and a G 2  filter section  4014   g   2 , a B 2  filter section  4014   b   2 , and a R 2  filter section  4014   r   2 , which constitute a second filter group for outputting narrowband surface-sequential light of discrete spectral characteristics, capable, as shown in  FIG. 73 , of extracting the desired depth layer tissue information, are arranged in the inner radial part. 
     Then, as shown in  FIG. 70 , the rotating filter  4014  is rotated in accordance with the control circuit  4017  driving and controlling a rotating filter motor  4018 , and movement in the radial direction (movement, which is perpendicular to the optical path of the rotating filter  4014 , and which selectively moves the first filter group and second filter group of the rotating filter  4014  in the optical path) is carried out by a mode switching motor  4019  in accordance with a control signal from a mode switching circuit  4042  inside the video processor  4007 , which will be explained hereinbelow. 
     Furthermore, power is supplied from a power unit  4010  to the xenon lamp  4011 , diaphragm device  4013 , rotating filter motor  4018 , and mode switching motor  4019 . 
     The video processor  4007  includes a CCD drive circuit  4020  for driving the CCD  4002 ; an amplifier  4022  for amplifying an image-capturing signal, which is an image of a body cavity tissue captured by the CCD  4002  via an objective optical system  4021 ; a processing circuit  4023 , which performs correlated double sampling and noise removal for an image-capturing signal through the amplifier  4022 ; an A/D converter  4024  for converting an image-capturing signal that has passed through the processing circuit  4023  to digital signal image data; a white balance circuit (W.B.)  4025  for performing white balance processing on the image data from the A/D converter  4024 ; a selector  4026  and synchronization memories  4027 ,  4028 ,  4029  for synchronizing surface-sequential light via the rotating filter  4014 ; an image processing circuit  4030  for reading out the respective image data of the surface-sequential light stored in the synchronization memories  4027 ,  4028 ,  4029 , and performing gamma correction processing, contour highlight processing, and color processing; D/A circuits  4031 ,  4032 ,  4033  for converting image data from the image processing circuit  4030  to analog signals; an encoding circuit  4034  for encoding image data from the image processing circuit  4030 ; and a timing generator (T.G.)  4035  for inputting from the control circuit  4017  of the light-source apparatus  4004  a synchronization signal synchronized to the rotation of the rotating filter  4014 , and outputting various timing signals to the above-described respective circuits. 
     Further, a mode-switching switch  4041  is provided to the electronic endoscope  4002 , and the output of the mode-switching switch  4041  is outputted to a mode-switching circuit  4042  inside the video processor  4007 . The mode-switching circuit  4042  of the video processor  4007  outputs control signals to the white balance circuit (W.B.)  4025 , a light modulation circuit  4043 , a light modulation control parameter switching circuit  4044 , and the mode-switching motor  4019  of the light-source apparatus  4004 . The light modulation control parameter switching circuit  4044  outputs a light modulation control parameter corresponding to the first filter group and the second filter group of the rotating filter  4014  to the light modulation circuit  4043 , and the light modulation circuit  4043  performs proper brightness control by controlling the diaphragm device  4013  of the light-source apparatus  4004  based on the control signal from the mode-switching circuit  4042  and the light modulation control parameter from the light modulation control parameter switching circuit  4044 . 
     As shown in  FIG. 74 , in most cases, for example, body cavity tissue  4051  has an absorbent distributed structure of blood vessels and the like that differ in the depth direction. In the vicinity of the superficial portion of the mucous membrane, mainly capillary vessels  4052  are distributed in large numbers, and in the intermediate layer, which is deeper than the superficial layer, blood vessels  4053  that are larger than capillary vessels are distributed in addition to capillary vessels, and in yet a deeper layer, even larger blood vessels  4054  are distributed. 
     Meanwhile, the invasion depth in the depth direction of light relative to a body cavity tissue  4051  is dependent on the wavelength of the light, and when illumination light including the visible region is a short wavelength like that of blue (B), as shown in  FIG. 75 , the light only penetrates as far as the vicinity of the superficial layer as a result of the absorption characteristics and scattering characteristics of the living tissue, is subjected to absorption and scattering in that depth range, and the light that exits from the surface is observed. Further, in the case of green (G) light, which has a longer wavelength than blue (B) light, the light penetrates deeper than the range to which the blue (B) light penetrated, is subjected to absorption and scattering in that range, and the light that exits from the surface is observed. Furthermore, red (R) light, which has a longer wavelength than green (G) light, reaches an even deeper range. 
     At ordinary observation, the mode switching circuit  4042  inside the video processor  4007  controls the mode switching motor  4019  via a control signal such that the R 1  filter  4014   r   1 , G 1  filter  4014   g   1 , and B 1  filter  4014   b   1 , which are the first filter group of the rotating filter  4014 , are located in the optical path of the illumination light. 
     As shown in  FIG. 72 , because the respective wavelength regions of the R 1  filter  4014   r   1 , G 1  filter  4014   g   1 , and B 1  filter  4014   b   1  overlap one another at ordinary observation of a body cavity tissue  4051 , (1) a band image including shallow layer and intermediate layer tissue information, which includes numerous tissue information of the shallow layer as shown in  FIG. 76 , is captured in an image-capturing signal, which is an image captured by the CCD  4004  via the B 1  filter section  4014   b   1 ; (2) further, a band image including shallow layer and intermediate layer tissue information, which includes numerous tissue information of the intermediate layer as shown in  FIG. 77 , is captured in an image-capturing signal, which is an image captured by the CCD  4004  via the G 1  filter section  4014   g   1 ; and (3) in addition, a band image including intermediate layer and deep layer tissue information, which includes numerous tissue information of the deep layer as shown in  FIG. 78 , is captured in an image-capturing signal, which is an image captured by the CCD  4004  via the R 1  filter section  4014   r   1 . 
     Then, an endoscopic image of a desired or natural color reproduction can be obtained as the endoscopic image by the video processor  4007  synchronizing the RGB image-capturing signals and performing signal processing. 
     Meanwhile, when the mode-switching switch  4041  of the electronic endoscope  4003  is pressed, the signal is inputted to the mode switching circuit  4042  of the video processor  4007 . By outputting a control signal to the mode switching motor  4019  of the light-source apparatus  4004 , the mode switching circuit  4042  drives the rotating filter  4014  relative to the optical path so as to move the first filter group of the rotating filter  4014 , which was in the optical path during ordinary observation, and position the second filter group in the optical path. 
     As shown in  FIG. 73 , because the G 2  filter section  4014   g   2 , B 2  filter section  4014   b   2 , and R 2  filter section  4014   r   2  change the illumination light to narrowband surface-sequential light of discrete spectral characteristics, and their respective wavelength regions do not overlap when body cavity tissue  4051  is being observed under narrowband light using the second filter group, (4) a band image including tissue information of the shallow layer as shown in  FIG. 79  is captured in an image-capturing signal, which is an image captured by the CCD  4004  via the B 2  filter section  4014   b   2 ; (5) a band image including tissue information of the intermediate layer as shown in  FIG. 80  is captured in an image-capturing signal, which is an image captured by the CCD  4004  via the G 2  filter section  4014   g   2 , and (6) furthermore, a band image including tissue information of the deep layer as shown in  FIG. 81  is captured in an image-capturing signal, which is an image captured by the CCD  4004  via the R 2  filter section  4014   r   2 . 
     The white balance circuit  4025  includes a white balance correction unit  4080 , selector  4081 , ordinary-light correction value storage unit  4082 , look-up table (LUT)  4083 , and narrowband-light correction value storage unit  4084 , as shown in  FIG. 82 . 
     White balance at ordinary light is achieved prior to an examination using the endoscope apparatus  4001  by attaching a white cap (not shown in the figure) to the distal end of the electronic endoscope  4003 . 
     In the white balance circuit  4025 , ordinary surface-sequential R/G/B signals, which are image data from the A/D converter  4024  when the white cap is attached, are inputted to the white balance correction unit  4080 , white balancing is performed for the ordinary surface-sequential R/G/B signals, and white-balance ordinary-light correction values are stored in the ordinary-light correction value storage unit  4082  by way of the selector  4081 , and, in addition, white-balanced R′/G′/B′ signals are outputted to the selector  4026 . 
     A narrowband-light correction value, which is based on the ordinary-light correction value, is then read out from the LUT  4083 , and stored in the narrowband-light correction value storage unit  4084  in the white balance circuit  4025 . 
     Specifically, in the white balance correction unit  4080 , correction values for R and B are calculated from the ratios G/R and G/B of the average values of the ordinary surface-sequential R/G/B signals, and if the observation mode detected by the mode-switching circuit  4042  is the ordinary-light mode, an ordinary-light correction value is stored in the ordinary-light correction value storage unit  4082 , and if the observation mode detected by the mode-switching circuit  4042  is the narrowband-light mode, a narrowband-light correction value is determined from the ordinary-light correction value and LUT  4083 , and stored in the narrowband-light correction value storage unit  4084 . A correction value is sent to the white balance correction unit  4080  from either the ordinary-light correction value storage unit  4082  or the narrowband-light correction value storage unit  4084  in accordance with the observation mode detected by the selector  4081 , the correction values are multiplied by the white balance correction unit  4080 , and R′ and B″ signals are outputted. The G signal is outputted as-is at this time. 
     Furthermore, the LUT  4083  stores a narrowband-light correction value based on an ordinary-light correction value, but the present invention is not limited to this. As shown in  FIG. 83 , the configuration can also be such that a correction value coefficient k based on an ordinary-light correction value is stored in the LUT  4083 , a narrowband-light correction value is computed by a narrowband-light correction value computation unit  4085  using the equation:
 
narrowband-light correction value= k ×ordinary-light correction value
 
and stored in the narrowband-light correction value storage unit  4084 . Furthermore, k is a constant.
 
     Thus, in the present embodiment, since correction is performed by calculating a narrowband-light correction value from the correction value for an ordinary light, the narrowband light does not need to undergo white balancing, making it possible to simplify operation, and to reliably avoid poor color reproduction due to an operational error. 
     Furthermore, in the endoscope apparatus  4001  of the above-described embodiment, the explanation gives as an example a surface-sequential-type endoscope apparatus in which the light-source apparatus  4004  supplies surface-sequential light, and the video processor  4007  synchronizes surface-sequential image information to create an image, but the present invention is not limited to this, and is also applicable to a synchronous-type endoscope apparatus. 
     That is, as shown in  FIG. 84 , a synchronous-type endoscope apparatus  4001   a , which includes a light-source apparatus  4004   a  for supplying white light; an electronic endoscope  4003   a  including a color chip  4100  on the front face of the image-capturing surface of the CCD  4002 ; and a video processor  4007   a , which performs signal processing of an image-capturing signal from the electronic endoscope  4003   a , can also apply the present embodiment. 
     In the light-source apparatus  4004   a , white light from the xenon lamp  4011  passes through the heat cutting filter  4012 , the quantity of light is controlled by the diaphragm device  4013 , and the white light is outputted to the incident surface of the light guide  4015 , which is arranged inside the electronic endoscope  4003   a . A narrowband interference filter  4014   a , which converts the white light to narrowband light of discrete spectral characteristics as shown in  FIG. 73 , is removably provided in the optical path. 
     In the electronic endoscope  4003   a , an image of body cavity tissue  4051  is captured by the CCD  4002  through the color chip  4100 . 
     In the video processor  4007   a , image data from the A/D converter  4024  is separated into a luminance signal Y and color difference signals Cr, Cb by the Y/C separation circuit  4101 , converted to RGB signals by the RGB matrix circuit  4102 , and outputted to the white balance circuit  4025 . The remaining configuration and operations are the same as the endoscope apparatus of  FIG. 70 . 
     Then, in the white balance circuit  4025 , as shown in  FIG. 85 , white balance is achieved for each signal of the RGB signals from the RGB matrix circuit  4102 . The white balance acquisition method at this time is the same as for the present embodiment. 
     Further, as shown in  FIG. 86 , the configuration is such that a scope ID storage unit  4110 , which stores a scope ID including various scope information to include an ordinary-light correction value, is provided in the electronic endoscope  4003 , and by outputting the ordinary-light correction value in the scope ID to the white balance circuit  4025 , as shown in  FIG. 87 , the ordinary light correction storage unit  4082  in the white balance circuit  4025  reads out a narrowband-light correction value from the LUT  4083  using the ordinary-light correction value, and stores the value in the narrowband-light correction value computation unit  4085 . 
     Furthermore, as shown in  FIG. 88 , a correction coefficient k, which is based on the ordinary-light correction value in the scope ID outputted to the white balance circuit  4025 , can be stored in the LUT  4083 , a narrowband-light correction value can be computed by the narrowband-light correction value computation unit  4085  using he above-mentioned equation:
 
narrowband-light correction value= k ×ordinary-light correction value
 
and the narrowband-light correction value may be stored in the narrowband-light correction value storage unit  4084 . Furthermore, k is a constant.
 
     Furthermore, in the endoscope of  FIG. 86 , the explanation gives as an example a surface-sequential-type endoscope, but the present invention is not limited to this, and a synchronous type is also applicable. 
     The present invention is not restricted to the embodiments described hereinabove, and various modifications and changes are possible within a scope that does not alter the gist of the present invention.