Patent Publication Number: US-8970685-B2

Title: Endoscope apparatus

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an endoscope apparatus which can perform special light observation using broadband light, such as white illumination light, and specific narrowband light. 
     In recent years, an endoscope apparatus which can perform so-called special light observation which irradiates specific narrow wavelength band light (narrowband light) onto a mucosal tissue of a living body and acquires tissue information at a desired depth of the body tissue is utilized. This type of endoscope apparatus can simply visualize living body information which is not acquired in, for example, normal observation images, such as enhancement of the surface layer fine structure of a new blood vessel generated in a mucosal layer or a submucosal layer, and a lesional part. For example, when an observation target is a cancerous lesional part, a fine blood vessel of a tissue surface layer or the state of fine structure can be observed in more detail if blue (B) narrowband light is irradiated on a mucosal tissue. Therefore, the lesional part can be more exactly diagnosed. 
     Even in this special light observation as well as the normal light (broadband light) observation, it is necessary to perform white balance processing on an acquired captured image in order to stabilize the reproducibility of color tone and to perform more exact diagnosis. 
     JP 2006-68321 A discloses an endoscope apparatus which can perform white balance processing in a short time in the normal light observation and the special light observation, respectively. 
     In the special light observation, when the distance between a diseased tissue and the irradiation position of the special light is short, a fine blood vessel or fine structure of a tissue surface layer which can be brightly viewed without difficulty can be imaged. However, there is a problem in that, as the distance increases, a captured image becomes dark and is not easily seen. Generally, a measure for increasing irradiation light quantity is taken. However, there is a limit to an increase in the irradiation light quantity, particularly, an increase in the light quantity of special light. There is a problem in that, if an attempt to compensate for the shortage of the light quantity of special light with normal light is made, the tint of a captured image changes. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an endoscope apparatus in which a user does not need to adjust irradiation light quantity intentionally while confirming a captured image in both of normal light observation and special light observation, and a captured image which is bright and has stable tint can always be obtained without being limited by an imaging distance with respect to the observation of the structure or components of living bodies, such as a surface layer fine blood vessel. 
     In order to achieve the above-mentioned objects, the resent invention provides an endoscope apparatus comprising: 
     a first light source section that irradiates first narrowband light with a predetermined wavelength bandwidth narrow-banded according to the spectral characteristics of the structure or components of a living body used as an object; 
     a second light source section that irradiates second narrowband light with a wavelength band different from the first narrowband light or broadband light with a broad wavelength band including visible light; 
     a light source control unit which controls the irradiation and irradiation light quantity of the first narrowband light from the first light source section, and the irradiation and irradiation light quantity of the second narrowband light or broadband light from the second light source section, respectively; 
     an imaging unit which obtains a captured image of the object to output captured image information, using return light from the object, of the first narrowband light and the second narrowband light or broadband light sequentially or simultaneously irradiated to the object; 
     a luminance value calculating unit which calculates the luminance value of the captured image from the captured image information imaged by the imaging unit; 
     a light source light quantity changing unit which changes the irradiation light quantity of the first narrowband light from the first light source section, and the irradiation light quantity of the second narrowband light or broadband light from the second light source section, according to the luminance value calculated in the luminance value calculating unit; 
     a white balance adjustment value calculating unit which calculates a white balance adjustment value for taking the white balance of the captured image from the irradiation light quantities, changed in the light source light quantity changing unit, of the first light source section and the second light source section which perform irradiation currently; and 
     a gain adjusting unit which adjusts the gain of the imaging unit so that the white balance of the captured image becomes a basis white balance according to the white balance adjustment value calculated in the white balance adjustment value calculating unit. 
     Further, preferably, the basis white balance is a white balance of the captured image obtained when a white plate is imaged with the irradiation light quantity of the first light source section and the irradiation light quantity of the second light source section being maximized, respectively. 
     Further, preferably, the light source light quantity changing unit is the unit which changes the ratio of the irradiation light quantity of the first narrowband light from the first light source section and the irradiation light quantity of the second narrowband light from the second light source section; and 
     the light source light quantity changing unit is the unit which changes the ratio of the irradiation light quantity of the first narrowband light from the first light source section and the irradiation light quantity of the broadband light from the second light source section. 
     Further, preferably, the light source light quantity changing unit increases the ratio of the irradiation light quantity from the first light source section as the calculated luminance value becomes large, and increases the ratio of the irradiation light quantity from the second light source section as the calculated luminance value becomes small, thereby setting the calculated luminance value to a predetermined luminance value. 
     Further, preferably, the light source light quantity changing unit gradually changes the irradiation light quantity of the first narrowband light from the first light source section according to the luminance value of the captured image; and 
     the light source light quantity changing unit continuously changes the irradiation light quantity of the first narrowband light from the first light source section according to the luminance value of the captured image. 
     Further, preferably, if the basis white balances are [R_base, G_base, B_base], the ratio of the irradiation light quantity of the first light source section and the irradiation light quantity of the second light source section is α:1−α, the white balances of the first light source section are [R — 1, G — 1, B — 1], and the white balances of the second light source section are [R — 2, G — 2, B — 2], the gains [WB_gainR, WB_gainG, WB_gainB] of the imaging element adjusted by the gain adjusting unit are expressed by the following formulas.
 
 WB _gain R =(α R   — 1+(1−α) R   — 2)/ R _base
 
 WB _gain G =(α G   — 1+(1−α) G   — 2)/ G _base
 
 WB _gain B =(α B   — 1+(1−α) B   — 2)/ B _base
 
     The present invention also provides an endoscope apparatus, further comprising: 
     an image processing section which performs predetermined image processing on the captured image information,
         wherein the image processing section has a color conversion coefficient table showing the relationship between the ratio of the irradiation light quantity of the first light source section and the irradiation light quantity of the second light source section which are obtained in advance, and a color conversion coefficient for adjusting the tint of the captured image so that image processing is performed, and thereby, the white balance of the captured image does not change, and   wherein the image processing section selects the color conversion coefficient from the color conversion coefficient table on the basis of the ratio of the irradiation light quantity of the first light source section and the irradiation light quantity of the second light source section adjusted by the light source light quantity changing unit.       

     Further, preferably, the first light source section includes a broadband light source which emits broadband light, and a first color filter which transmits only the first narrowband light from the broadband light emitted from the broadband light source; 
     the second light source section includes the broadband light source and a second color filter that transmits only the second narrowband light from the broadband light emitted from this broadband light source; and 
     the light source light quantity changing unit is the unit which switches at least one of the first color filter and the second color filter to a color filter with a different half-value width. 
     According to the endoscope apparatus of the invention, the light emission conditions of the special light source and the white illumination light source are controlled in order so that the light quantity of the return light detected with the imaging element always becomes equal to or more than a predetermined value in the normal light observation and the special light observation. Additionally, when normal light observation and special light observation are performed in order to perform predetermined image processing for adjusting tint in the image processing section according to the light emission conditions of the special light source and the white illumination light source, for example, even if imaging is performed apart from a lesional part or even if imaging is performed close to a lesional part, a user does not need to adjust the light emission conditions of the light sources and the tint of a captured image intentionally while confirming the captured image, and a captured image which has stable tint can always be obtained without being limited by an imaging distance, particularly, in the special light observation of a lesional part, a surface layer fine blood vessel, or the like as well as in the normal light observation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram schematically showing the overall configuration of a first embodiment of an endoscope apparatus of the invention. 
         FIG. 2  is a graph showing emission spectra of a blue-violet laser beam irradiated from a blue-violet laser light source and white light from a blue laser beam irradiated from a blue laser light source and fluorescent light from an excited fluorescent body, those light sources being used for a light source section of the endoscope apparatus shown in  FIG. 1 . 
         FIG. 3  is a block diagram showing signal processing systems of respective sections including the detailed configuration of one example of a processor of the endoscope apparatus shown in  FIG. 1 . 
         FIG. 4  is a graph showing one example of a color conversion table provided in a special light color conversion section of a special light image processing section shown in  FIG. 3 . 
         FIG. 5  is a flowchart showing an example of the operation of the first embodiment of the endoscope apparatus of the invention. 
         FIG. 6  is a block diagram schematically showing the overall configuration of a second embodiment of the endoscope apparatus of the invention. 
         FIG. 7  is a front view showing one example of a filter set including first and second color filters of the endoscope apparatus shown in  FIG. 6 . 
         FIG. 8A  is graph showing an example of the spectral characteristics of a blue filter with a narrow half-value width which is the first color filter and a green filter with a narrow half-value width which is the second color filter, and  FIG. 8B  is a graph showing an example of the spectral characteristics of a blue filter with a wide half-value width which is the first color filter, and a green filter with a wide half-value width which is the second color filter. 
         FIG. 9  is a block diagram showing signal processing systems of respective sections including the detailed configuration of one example of a processor of the endoscope apparatus shown in  FIG. 6 . 
         FIG. 10  is a flowchart showing an example of the operation of the second embodiment of the endoscope apparatus of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An endoscope apparatus of the invention will be described below in detail on the basis of preferred embodiments shown in the accompanying drawings. 
       FIG. 1  is a block diagram schematically showing the overall configuration of a first embodiment of the endoscope apparatus of the invention. 
     As shown in this drawing, the endoscope apparatus  10  of the invention has an endoscope  12 , a light source device  14 , a processor  16 , and an input and output section  18 . Here, the light source device  14  and the processor  16  constitute a control device of the endoscope  12 , and the endoscope  12  is optically connected to the light source device  14 , and is electrically connected to the processor  16 . Additionally, the processor  16  is electrically connected to the input and output section  18 . The input and output section  18  has a display section (monitor)  38  which displays image information or the like as output, a recording section (recording device)  42  (refer to  FIG. 3 ) which outputs image information or the like, and an input section (mode switching section)  40  which functions as UI (user interface) which receives input operations, such as mode switching between a normal observation mode (also referred to as a normal light mode) and a special light observation mode (also referred to as a special light mode), and function settings. 
     The endoscope  12  is an electronic endoscope which has an illumination optical system which irradiates illumination light from the distal end thereof, and an imaging optical system which images a region to be observed. In addition, although not shown, the endoscope  12  includes an endoscope insertion part inserted into a subject, a manipulation part which performs curving manipulation of the distal end of the endoscope insertion part, and manipulation for observation, and connector parts which detachably connect the endoscope  12  to the light source device  14  and the processor  16  of the control device. Moreover, although not shown, various channels, such as a forceps channel which allows a treatment tool or the like for tissue sampling to be inserted thereinto, and air supply and water supply channels, are provided inside the manipulation part and the endoscope insertion part. 
     As shown in  FIG. 1 , a fluorescent body  24 , though the details thereof will be described below, which constitutes the illumination optical system and constitutes a white light source, is provided in an irradiation port  28 A which allows light to be irradiated to a region to be observed therethrough, at the distal end portion of the endoscope  12 . An imaging element (sensor)  26 , such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal-Oxide Semiconductor) image sensor serving as an imaging unit which acquires the image information of a region to be observed, are arranged at a light-receiving part  28 B adjacent to the irradiation port  28 A. A cover glass or a lens (not shown) which constitutes the illumination optical system is arranged at the irradiation port  28 A of the endoscope  12 , a cover glass or a lens (not shown) which constitutes the illumination optical system is arranged at the light-receiving part  28 B, and an objective lens unit (not shown) which constitutes the imaging optical system is arranged at a light-receiving surface of the imaging element  26  of the light-receiving part  28 B. 
     The endoscope insertion part is made curvable by the manipulation of the manipulation part, can be curved in arbitrary directions and at arbitrary angles according to parts of a subject in which the endoscope  12  is used, and can direct the irradiation port  28 A and the light-receiving part  28 B, that is, the observation direction of the imaging element  26 , to a desired observation part. 
     In addition, although it is preferable that the imaging element  26  be a color imaging sensor or a complementary-color sensor including a color filter (for example, an RGB color filter or a complementary-color filter) in a light-receiving region, the RGB color imaging sensor is more preferable. 
     The light source device  14  includes as light-emitting sources, a blue-violet laser light source ( 405 LD)  32  with a central wavelength of 405 nm which is used as a special light source in the special light mode, and a blue laser light source ( 445 LD)  34  with a central wavelength of 445 nm which is used as a light source for white illumination light in both the normal light mode and the special light mode. The blue-violet laser light source  32  irradiates a blue-violet laser beam as first narrowband light, and the blue laser light source  34  irradiates a blue laser beam as second narrowband light. In addition, since the blue-violet laser beam with a central wavelength of 405 nm from the blue-violet laser light source  32  is narrowband light with a wavelength bandwidth which is narrow-banded according to the spectral characteristics of the structure or components of a living body, preferably, in conformity with the characteristics, the detectability of the structure or components of the living body is excellent. 
     The light emitted from a semiconductor light-emitting element of each of the light sources  32  and  34  is individually controlled by a light source control unit  48  (refer to  FIG. 3 ), and the light emission conditions of each of the light sources  32  and  34 , that is, the light quantities and the light quantity ratios of the illumination light of the blue-violet laser light source  32  and the illumination light of the blue laser light source  34  can be changed. 
     The blue-violet laser light source  32  and the blue laser light source  34  can use a broad area type InGaN-based laser diode, and can also use an InGaNAs-based laser diode or a GaNAs-based laser diode. Additionally, the above light sources may be configured using light emitters, such as a light-emitting diode. 
     The laser beams irradiated from the blue-violet laser light source  32  and the blue laser light source  34  are input to optical fibers  22 , respectively, by condensing lenses (not shown), and are transmitted to a connector part via a multiplexer (not shown). In addition, the invention is not limited thereto, and may have a configuration in which the laser beams from the blue-violet laser light source  32  and the blue laser light source  34  are respectively delivered directly to the connector part without using the multiplexer. 
     A blue-violet laser beam with a central wavelength of 405 nm and a blue laser beam with a central wavelength of 445 nm are multiplexed, and a laser beam transmitted to the connector part propagates to a distal end portion of the endoscope  12  by the optical fiber  22  which constitutes the illumination optical system. Then, the blue laser beam excites the fluorescent body  24  which is a wavelength conversion member arranged at light irradiation end of the optical fiber  22 , at the distal end of the endoscope  12 , thereby making the fluorescent body emit fluorescence. Additionally, a portion of the blue laser beam is transmitted through the fluorescent body  24  as it is. Although a portion of the blue-violet laser beam excites the fluorescent body  24 , most of the beam is transmitted through the fluorescent body  24  without exciting the fluorescent body and becomes illumination light (so-called narrowband light) with a narrowband wavelength. 
     The blue-violet laser light source  32  constitutes a first light source section of the invention, and the blue laser light source  34  and the fluorescent body  24  constitute a second light source section of the invention. 
     The optical fiber  22  is a multimode fiber, and a fine-diameter fiber cable whose core diameter is 105 μm, cladding diameter is 125 μm, and for which a diameter including a protective layer serving as an outer skin is 0.3 to 0.5 mm can be used as an example. 
     The fluorescent body  24  is configured so as to include a plurality of kinds of fluorescent bodies (for example, fluorescent bodies, such as a YAG-based fluorescent body or BAM (BaMgAl 10 O 17 ) fluorescent body) which absorb a portion of the blue laser beam and a portion of the blue-violet laser beam, and are excited to emit green to yellow light. Thereby, the green to yellow excitation light having the blue laser beam and the blue-violet laser beam as excitation light, and the blue laser beam and the blue-violet laser beam which are transmitted through the fluorescent body  24  without being absorbed thereby are put together, and become white (pseudo-white) illumination light. If the semiconductor light-emitting element which emits a blue laser beam with a central wavelength of 445 nm is used as an excitation light source as this configuration example, high-intensity white light can be obtained at high luminous efficiency, the intensity of the white light can be easily adjusted, and changes in color temperature and chromaticity of the white light can be suppressed to be low. 
     The fluorescent body  24  can prevent superposition of noise becoming an obstacle to imaging or occurrence of flickering when moving image display is performed, due to a speckle caused by the coherency of a laser beam. Additionally, the fluorescent body  24  is preferably made of a material having small absorption and large scattering of infrared light with respect to the grain sizes of the fluorescent material itself and the filler material in consideration of the refractive index difference between a fluorescent material which constitutes the fluorescent body, and a fixing and solidifying resin becoming a filler material. Thereby, a scattering effect is enhanced without reducing light intensity with respect to red light or infrared light, and optical loss becomes small. 
       FIG. 2  is a graph showing emission spectra of a blue-violet laser beam from the blue-violet laser light source  32  and a blue laser beam from the blue laser light source  34  combined with fluorescent light which was converted from the blue laser beam by the fluorescent body  24 . The blue-violet laser beam is expressed by an emission line (profile A) with a central wavelength of 405 nm, is the narrowband light of the invention, and is used mainly as special light. Additionally, the blue laser beam is expressed by an emission line with a central wavelength of 445 nm, and fluorescent light from the fluorescent body  24  caused by the blue laser beam has a spectral intensity distribution in which emission intensity increases in a wavelength band of approximately 450 nm to 700 nm. The above-described white light is formed by a profile B including the fluorescent light and the blue laser beam, and is used mainly as normal light. The normal light which is white light is broadband light with a broad wavelength band including visible light. In addition, although not shown, the fluorescent body  24  is excited even by the blue-violet laser beam to irradiate fluorescent light with a light quantity of about 1/20 of the light quantity based on the blue laser beam, and form broadband light. 
     Here, there are a number of 405 nm narrowband light components in the blue-violet laser beam with a central wavelength of 405 nm emitted from the blue-violet laser light source  32  and the accompanying fluorescent light from the fluorescent body  24 , and the observation (acquisition of information on a surface layer tissue) of a surface layer tissue is excellent. On the other hand, since there are few fluorescent light components from the fluorescent body  24 , the irradiation light quantity of the white light used for the imaging of a background is not increased. Hence, when the distance to an object is small, the irradiation light quantity of the white light serving as a background is sufficient. However, when the distance to an object is great, the irradiation light quantity of the white light is insufficient in the fluorescent light by the blue-violet laser beam. 
     Additionally, although the blue laser beam with a central wavelength of 445 nm emitted from the blue laser light source  34  and the accompanying fluorescent light from the fluorescent body  24  are inferior to the blue-violet laser beam in terms of the observation of a surface layer tissue, the blue laser beam can excite the fluorescent body  24  strongly to increase the irradiation light quantity of the white light as a background. Hence, even when the distance to an object is far, the light quantity of the white light can be sufficiently secured. 
     Therefore, when the distance from an object is far, the blue laser light source  34  can be used in order to compensate for the shortage of the light quantity of the white light obtained from the blue-violet laser beam from the blue-violet laser light source  32 . 
     Additionally, the white light in the invention is not strictly limited to that including all the wavelength components of visible light, for example, may include the light of a specific wavelength band, such as R, G, and B, including the above-described pseudo-white light. For example, the white light broadly includes the light including wavelength components from green to red, the light including wavelength components from blue to green, or the like. 
     In the endoscope apparatus  10 , the emission intensity of the profile A and the profile B can be controlled so as to be relatively increased or decreased by the light source control unit  48 , to produce illumination light with arbitrary luminance balance. In addition, in the endoscope apparatus  10  of the invention, only the light of the profile B is used in the normal light mode. In the special light mode, the light of the profile A and the fluorescent light (not shown) based on the light of the profile A are used in principle and the light of the profile B is superposed in order to compensate for the shortage of the light quantity of the fluorescent light which is not shown. 
     As described above, illumination light made up of the white light obtained from the narrowband light (profile A) based on the blue-violet laser beam from the blue-violet laser light source  32  and the fluorescent light (not shown) from the fluorescent body  24 , and illumination light (profile B) made up of the white light obtained from the blue laser beam from the blue laser light source  34  and the fluorescent light from the fluorescent body  24  are irradiated toward the region of an object to be observed from the irradiation port  28 A at the distal end portion of the endoscope  12 . The return light from the region to be observed which is irradiated with the illumination light is focused on the light-receiving surface of the imaging element  26  via the light-receiving part  28 B, and the region to be observed is imaged by the imaging element  26 . 
     Image signals of a captured image output from the imaging element  26  after imaging are input to an image processing system  36  of the processor  16  through a scope cable  30 . 
     Next, the image signals of the image captured by the imaging element  26  in this way are subjected to image processing by a signal processing system including the image processing system  36  of the processor  16 , are output to a monitor  38  or a recording device  42 , and are provided for user&#39;s observation. 
       FIG. 3  is a block diagram showing signal processing systems of respective sections including the detailed configuration of one example of the processor of the endoscope apparatus of the invention. 
     As shown in this drawing, the signal processing system of the endoscope apparatus  10  has a signal processing system of the endoscope  12 , a signal processing system of the light source device  14 , a signal processing system of the processor  16  (image processing system  36 ), and the monitor  38 , an input section (mode switching section)  40  and the recording device  42  of the input and output section  18 . 
     The signal processing system of the endoscope  12  is a signal processing system for image signals of a captured image from the imaging element  26  after imaging, and has a CDS•AGC circuit  44  for performing correlated double sampling (CDS) or automatic gain control (AGC) on the captured image signals which are analog signals, and an A/D converter  46  which converts analog image signals subjected to sampling and gain control in the CDS•AGC circuit  44  into digital image signals. The digital image signals which are A/D converted in the A/D converter  46  are input to the image processing system  36  of the processor  16  via a connector part. 
     Additionally, the signal processing system of the light source device  14  has light source control unit  48  which performs ON/OFF control and light quantity control (intensity control) of the blue-violet laser light source  32  and the blue laser light source  34 . In the invention, the light quantity includes intensity. In a first embodiment, the light source control unit  48  principally changes the irradiation intensity of a light source to change the irradiation light quantity thereof. 
     Here, the light source control unit  48  turns on the blue-violet laser light source  32  according to a light source ON signal accompanying the starting-up of the endoscope apparatus  10 , performs ON/OFF control of the blue-violet laser light source  32  according to a switching signal between the special light mode and the normal light mode from the mode switching section  40 , or controls the irradiation light quantities of the laser light sources by controlling the emission intensity of the blue-violet laser light source  32  and the blue laser light source  34 , that is, the current value of driving currents sent through the blue-violet laser light source  32  and the blue laser light source  34  through the light source control unit  48  by a light source light quantity changing unit  55  so that the luminance values of the aforementioned captured image signals become predetermined luminance values, according to the luminance values of captured image information calculated from a luminance value calculating unit  50  (as will be described below). Additionally, in the invention, the predetermined luminance values mean a predetermined range of luminance values suitable for observation of a captured image. 
     Moreover, the signal processing system of the processor  16  is the image processing system  36  (refer to  FIG. 1 ), and has the luminance value calculating unit  50 , a DSP (digital signal processor)  52 , a denoising circuit  54 , the light source light quantity changing unit  55 , a white balance adjustment value calculating unit  57 , a gain adjusting unit  59 , an image processing switching section (switch)  60 , a normal light image processing section  62 , a special light image processing section  64 , and an image display signal generating section  66 . 
     The luminance value calculating unit  50  calculates the light quantity of return light received in the imaging element (sensor)  26 , that is, the luminance values of a captured image, using digital image signals (captured image information) input via a connector from the A/D converter  46  of the endoscope  12 . Then, the calculated luminance values are output to the light source control unit  48  and the light source light quantity changing unit  55 . 
     The light source light quantity changing unit  55  receives information on the current value of currents that drive the blue-violet laser light source  32  and the blue laser light source  34  by the light source control unit  48 , and changes the irradiation light quantities and light quantity ratios of the blue-violet laser light source  32  and the blue laser light source  34  on the basis of the calculated luminance values. 
     For example, the instruction of reducing the irradiation light quantity of the blue laser light source  34  is issued to the light source control unit  48  so as to increase the irradiation light quantity of the blue laser light source  34  so that the blue laser beam which emits the fluorescent light to act as the white light increases if the luminance values of captured image information be small (dark) and so as to increase the ratio of the irradiation light quantity of the blue-violet laser light source  34  so that the light quantity ratios of the narrowband light is increased if the luminance values of captured image information be large (bright). Thereby, the luminance values of a captured image become predetermined luminance values suitable for observation. 
     Additionally, the information on the irradiation light quantities and light quantity ratios of the blue-violet laser light source  32  and the blue laser light source  34  in the light source light quantity changing unit  55  is also output to the white balance adjustment value calculating unit  57 , and is output to the special light image processing section  64  through the gain adjusting unit  59 . 
     The light source control unit  48  controls driving currents which flow into the blue-violet laser light source  32  and the blue laser light source  34 , and the irradiation light quantities of the light sources, on the basis of the information on the aforementioned luminance values, and the instruction from the light source light quantity changing unit  55 . 
     The irradiation light quantities may be controlled so as to be continuously changed according to the aforementioned luminance values, and so as to be gradually changed so that the blue-violet laser light source  32  and the blue laser light source  34  have predetermined irradiation light quantities, respectively, when the luminance values are in a predetermined range. 
     On the basis of the irradiation light quantities and light quantity ratios of the blue-violet laser light source  32  and the blue laser light source  34  in the light source light quantity changing unit  55 , the white balance adjustment value calculating unit  57  calculates the white balances when imaging is performed with illumination light, and calculates, as white balance gains, white balance adjustment values required in order to adopt the white balances when imaging is performed with illumination light, as basis white balances. 
     The white balances when imaging is performed with illumination light are calculated as [(αWB_R1+(1−α)WB_R2), (αWB_G1+(1−α)WB_G2), (αWB_B1+(1−α)WB_B2)], if the white balances when imaging is performed by the blue-violet laser light source  32  are [WB_R1, WB_G1, WB_B1], the white balances when imaging is performed by the blue laser light source  34  are [WB_R2, WB_G2, WB_B2], and the ratios (ratios of driving current values) between the irradiation light quantity of the blue-violet laser light source  32  and the irradiation light quantity of the blue laser light source  34  which are irradiated is α and 1−α, respectively. 
     Additionally, if the basis white balances are [WB_Rbase, WB_Gbase, WB_Bbase], the white balance gains required in order to adopt the white balances when imaging is performed with illumination light as the basis white balances can be calculated as follows:
 
 WB _gain R =(α WB   —   R 1+(1−α) WB   —   R 2)/ WB   —   R base
 
 WB _gain G =(α WB   —   G 1+(1−α) WB   —   G 2)/ WB   —   G base
 
 WB _gain B =(α WB   —   B 1+(1−α) WB   —   B 2)/ WB   —   B base
 
     In addition, as for the white balances when imaging is performed by the blue-violet laser light source  32  and the white balances when imaging is performed by the blue laser light source  34 , for example, a white plate may be installed so as to face the distal end of the endoscope before imaging of an object, the blue-violet laser light source  32  and the blue laser light source  34  may perform irradiation independently to perform imaging, and the white balances of the respective captured images (captured image information) obtained may be the white balances [WB_R1, WB_G1, WB_B1], and [WB_R2, WB_G2, WB_B2] when imaging is performed with the blue-violet laser light source  32  and the blue laser beam  34 . 
     Additionally, as for the basis white balances, for example, similarly to the above description, a white plate may be installed so as to face the distal end of an endoscope before the imaging of an object, illumination light may be irradiated with the irradiation light quantities of the blue-violet laser light source  32  and the blue laser light source  34  being the maximum to perform imaging of the white plate, and the white balances of the captured images obtained in this case may be the basis white balances [WB_Rbase, WB_Gbase, WB_Bbase]. 
     The white balances when imaging is performed by the blue-violet laser light source  32 , the white balances when imaging is performed by the blue laser beam  34 , and the basis white balances are stored in advance in the white balance adjustment value calculating unit  57 . 
     The gain adjusting unit  59  adjusts the white balances of the captured image information in the CDS•AGC circuit  44 , on the basis of the white balance gains [WB_gainR, WB_gainG, WB_gainB] calculated in the aforementioned white balance adjustment value calculating unit  57 . 
     Additionally, the calculated white balance gains may be output to the image processing section  62  and the special light image processing section  64 , and may be used for color conversion and special light color conversion. 
     Through the adjustment of white balances using the gain adjusting unit  59 , a captured image in which white balances are always stable can be obtained even if the luminance values of the captured image have changed. 
     The DSP  52  (digital signal processor) performs gamma correction and color correction processing on the digital image signals output from the A/D converter  46  after the luminance values of captured image signals (captured image information) is calculated by the luminance value calculating unit  50 . 
     The denoising circuit  54  performs a denoising method in image processing, such as a moving-average method or a median filter method, and removes noise from the digital image signals subjected to the gamma correction and color correction processing in the DSP  52 . 
     The digital image signals input to the processor  16  from the endoscope  12  in this way are subjected to preprocessing, such as gamma correction, color correction processing, and denoising, in the DSP  52  and the denoising circuit  54 . 
     The image processing switching section  60  is a switch which switches whether the preprocessed digital image signals are sent to the normal light image processing section  62  or the special light image processing section  64  in the subsequent stage, on the basis of the instruction (switching signal) from the mode switching section (input section) as will be described below. 
     In addition, in the invention, for the purpose of distinction, digital image signals before image processing using the normal light image processing section  62  and the special light image processing section  64  are referred to as an image signal, and digital image signals before and after image processing are referred to as image data. 
     The normal light image processing section  62  is a section which performs image processing for normal light suitable for the preprocessed digital image signals based on the white light (profile B) using the blue laser light source  34  and the fluorescent body  26 , in the normal optical mode, and has a color converter  68 , a color enhancing section  70 , and a structure enhancing section  72 . 
     The color converter  68  performs color conversion processing, such as matrix processing of 3×3, grayscale conversion processing, and three-dimensional LUT processing, on preprocessed RGB 3-channel digital image signals, and converts image signals into color-conversion-processed RGB image data. 
     The color enhancing section  70  gives a difference in tint between a blood vessel and a mucous membrane in a screen to enhance the blood vessel so as to be easily seen, and performs processing on the color-conversion-processed RGB image data while the screen is being viewed, for example, views the average tint of the full screen, and performs the processing of enhancing the tint in a direction in which the difference in tint between the blood vessel and the mucous membrane is given more than the average value. 
     The structure enhancing section  72  performs structure enhancement processing, such as sharpness or contour enhancement, on the color-enhanced RGB image data. 
     The RGB image data which has been subjected to the structure enhancement processing in the structure enhancing section  72  is input to the image display signal generating section  66  from the normal light image processing section  62  as image-processed RGB image data for normal light. 
     The special light image processing section  64  is a section which performs image processing for special light suitable for preprocessed digital image signals based on the blue-violet laser beam from the blue-violet laser light source  32  (profile A), and the white light (profile B) from the blue laser light source  34  and the fluorescent body  26 , in the special light mode, and has a special light color conversion section  74 , a color enhancing section  76 , and a structure enhancing section  78 . 
     The special light color conversion section  74  multiplies a G image signal of digital image signals of input preprocessed RGB3 channels by a predetermined coefficient to allocate the resulting value to R image data, and multiplies a B image signal by a predetermined coefficient to allocate the resulting values to B image data and G image data, respectively, thereby generating RGB image data, and then performs color conversion processing, such as 3×3 matrix processing, grayscale conversion processing, and three-dimensional LUT processing, on the generated RGB image data similarly to the color converter  68 . 
     Specifically, the special light converter  74  normalizes luminance values with respect to the R, G, and B image data after the allocation, and generates R norm , G norm , and B norm  image data. Next, the correction of the normalized R norm , G norm , and B norm  image data to the color tone according to light quantity ratios is performed. If the image data after the color tone correction is R adj , G adj , and B adj  image data, R adj , G adj , and B adj  image data after the color tone correction are obtained by the operation as shown in Formula (1). 
     
       
         
           
             
               
                 
                   
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     Here, K R , K G , and K B  are color conversion coefficients of respective colors, and are obtained according to the light quantity ratios of the blue-violet laser light source  32  and the blue laser light source  34  adjusted in the light source light quantity changing unit  55 . As shown in  FIG. 4 , the special light converter  74  includes a color conversion coefficient table  80  which determines the color conversion coefficients of respective colors corresponding to adjusted light quantity ratios, and determines the color conversion coefficients K R , K G , and K B  from the color conversion coefficient table  80  on the basis of the aforementioned light quantity ratios. The color conversion coefficients K R , K G , and K B  of the color conversion coefficient table  80  are set as R 00 ˜, G 00 ˜, and B 00 ˜ so as to correspond to the respective light quantity ratios, as shown in  FIG. 4 . By substituting the color conversion coefficients corresponding to the light quantity ratios adjusted in the light source light quantity changing unit  55  into Formula (1), the image data R adj , G adj , and B adj  subjected to color tone correction are obtained. 
     For example, when the ratio of the light quantity of the blue-violet laser light source  32  and the light quantity of the blue laser light source  34  which are controlled in the light source control unit  48  is 90:10, the color conversion coefficients are obtained as (K R , K G , K B )=(R 10 , G 10 , B 10 ) by the color conversion coefficient table shown in  FIG. 4 . 
     The color conversion coefficients are not limited to those expressed as the table shown in  FIG. 4 , and may be expressed by a numerical formula. Additionally, only a representative point may be quantified, and other points may be obtained by interpolation operation. 
     The color enhancing section  76 , similarly to the color enhancing section  70 , gives a difference in tint between a blood vessel and a mucous membrane in a screen to enhance the blood vessel so as to be easily seen, and performs processing on the color-conversion-processed RGB image data while viewing the screen, for example, views the average tint of the full screen, and performs the processing of enhancing the tint in a direction in which the difference in tint between the blood vessel and the mucous membrane is given more than the average value. 
     The structure enhancing section  78 , similarly to the structure enhancing section  72 , performs structure processing, such as sharpness or contour enhancement, on the color-enhanced RGB image data. 
     The RGB image data subjected to optimal frequency enhancement processing in the structure enhancing section  78  is output to the image display signal generating section  66  from the special light image processing section  64  as image-processed RGB image data for special light. 
     Additionally, as mentioned above, when the light quantity is insufficient and the irradiation light quantity of the blue laser light source  34  is increased, the light quantity for imaging is sufficient. However, the color tone of a captured image changes and information on a captured image regarding the fine structure of a surface layer blood vessel observed with special light also becomes less conspicuous. 
     Thus, the special light image processing section  64  may perform frame addition processing or binning processing, also in order to enhance a surface layer blood vessel on a captured image, in the preceding stage of the color converter  68 . 
     Here, the frame addition processing is generally the processing of adding a plurality of frames which generate one image in one frame, and the binning processing is the processing of unifying pixels which constitute an image in units of a plurality of pixels. 
     In addition, instead of the frame addition processing and binning processing, the charge storage time of the imaging element  26  may be lengthened in advance. Almost the same effect as the frame addition processing is obtained. 
     The image display signal generating section  66  converts the image-processed RGB image data input from the normal light image processing section  62  in the normal light mode and the image-processed RGB image data input from the special light image processing section  64  in the special light mode into display image signals for being displayed as a soft copy image in the monitor  38  or for being output as a hard copy image in the recording device  42 . 
     The monitor  38  displays, as a soft copy image, a normal light observation image based on display image signals which are obtained in the imaging element  26  by the irradiation of white light and subjected to the preprocessing and the normal light image processing in the processor  16 , in the normal light mode, and display, as a soft copy image, a special light observation image based on display image signals which are obtained in the imaging element  26  by the irradiation of special light in addition to white light and subjected to the preprocessing and the special light image processing in the processor  16 , in the special light mode. 
     The recording device  42  also outputs the normal light observation image obtained by the irradiation of white light as a hard copy image in the normal light mode, and outputs the special light observation image obtained by the irradiation of white light and special light as a hard copy image in the special light mode. 
     In addition, if required, the display image signals generated in the image display signal generating section  66  may be stored as image information in a storage section made up of memory or a storage device, though not shown. 
     On the other hand, the mode switching section (input section)  40  has mode switching buttons for performing switching between the normal light mode and the special light mode, and a mode switching signal from the mode switching section  40  is input to the light source control unit  48  of the light source device  14 . Here, although the mode switching section  40  is arranged as the input section  40  of the input and output section  18 , the mode switching section may be arranged at the processor  16 , the manipulation part of the endoscope  12 , or the light source device  14 . In addition, a switching signal from the mode switching section  40  is output to the light source control unit  48  and the image processing switching section  60 . 
     The endoscope apparatus  10  of the first embodiment of the invention is basically configured as described above. 
     Next, the operation of the endoscope apparatus  10  of the first embodiment of the invention will be described with reference to  FIG. 5 . 
     In the present embodiment, first, normal light observation shall be performed in the normal light mode. That is, the blue laser light source  34  is turned on, and normal light image processing is performed on captured image data based on white light in the normal light image processing section  64 . 
     Here, switching to the special light mode is performed by a user according to the steps shown in  FIG. 5 . A mode switching signal (special light ON) is output as the user operates the mode switching section  40 , and the image processing in the image processing switching section  60  is switched to the special light mode. Additionally, switching to the special light mode may be performed not by operating the mode switching section  40  but by operating the manipulation part (not shown) of the aforementioned endoscope  12  (S 10 ). 
     When switching to the special light mode is performed, a predetermined quantity of the first narrowband light (with a central wavelength of 405 nm) from the blue-violet laser light source  32 , and a predetermined quantity of the second narrowband light (with a central wavelength of 445 nm) from the blue laser light source  34  are simultaneously irradiated, and the first narrowband light, the second narrowband light, and the fluorescent light are irradiated toward an object from the distal end of the endoscope as illumination light (S 12 ). 
     The irradiated illumination light is reflected by the object, the return light is acquired by the imaging element  26  as captured image signals (captured image information), and the luminance values of the captured image signals acquired by the imaging element  26  are calculated in the luminance value calculating unit  50 . The luminance values of the calculated captured image signals are output to the light source light quantity changing unit  55  and the light source control unit  48  (S 14 ). 
     Then, the light source light quantity changing unit  55  adjusts the respective irradiation light quantities of the blue-violet laser light source  32  and the blue laser light source  34  and adjusts the light quantity ratios thereof so that the captured image is not too bright and is not too dark and the luminance values become predetermined luminance values, on the basis of the information on the luminance values calculated in the luminance value calculating unit  50  and the information on the irradiation light quantities and light quantity ratios from the blue-violet laser light source  32  and the blue laser light source  34  obtained from the light source control unit  48 . These adjustments are performed in practice by adjusting the values of driving currents which flows to the blue-violet laser light source  32  and the blue laser light source  34  through the light source control unit  48 . Then, the information on the adjusted irradiation light quantities and light quantity ratios is output to the light source control unit  48  and the white balance adjustment value calculating unit  57 , respectively (S 16 ). 
     Since Step S 14  and Step S 16  are performed according to changes in the luminance values, these steps are performed according to a change in the positional relationship between the distal end of the endoscope and the object. 
     Additionally, the white balance adjustment value calculating unit  57  first calculates the white balances of the captured image on the basis of the information on the aforementioned adjusted irradiation light quantities and light quantity ratios. The white balances, as mentioned above, are calculated on the basis of the white balances of the illumination light based on the blue-violet laser light source  32 , the white balances of the illumination light based on the blue laser light source  34 , and the irradiation light quantities and light quantity ratios of the blue-violet laser beam and the blue laser beam (S 18 ). 
     Then, white balance gains required in order to maintain the white balances are calculated from the calculated white balances and the basis white balances, and the white balance gains are adjusted in the CDS•AGC circuit  44  through the gain adjusting unit  59  (S 20 ). 
     After the irradiation light quantities and light quantity ratios from the blue-violet laser light source  32  and the blue laser light source  34  is changed by the light source light quantity changing unit  55 , and the white balance gains are adjusted by the gain adjusting unit  59 , imaging of an object is performed and captured image signals are acquired by the imaging element  26  (S 22 ). 
     If captured image signals are acquired again, the captured image signals are output to the luminance value calculating unit  50  through the CDS•AGC  44  and the A/D converter  46 , and the luminance values of the captured image (signals) are calculated. Thereafter, the captured image signals are output to the special light image processing section  64  through the DSP52 and the denoising circuit  54 . In the special light color conversion section  74  of the special light image processing section  64 , the color conversion coefficients K R , K G , and K B  used for special light color conversion, are set from the information on the aforementioned changed irradiation light quantities and light quantity ratios, and the color conversion coefficient table  80 , and the captured image signals input to the special light image processing section  64  are turned into predetermined RGB image data by the special light color conversion section  74 . In addition, image enhancement processing such as frame addition processing or the like may be performed before the special light color conversion. Additionally, the RGB image data is subjected to various image processing in the color enhancing section  76  and the structure enhancing section  78 , and is output to the image display signal generating section  66  (S 24 ). 
     The RGB image data output to the image display signal generating section  66  is converted into image display signals which can be displayed, is displayed on the monitor  38  as a special light image, and is recorded in the recording device  42  (S 26 ). 
     The above is the first embodiment of the invention. Next, a second embodiment of the invention will be described.  FIG. 6  is a block diagram schematically showing the overall configuration of a second embodiment of the endoscope apparatus of the invention. 
     As shown in  FIG. 6 , the constitutional differences between the second embodiment and the first embodiment are the configuration of the light source device  114 , and the fluorescent body  24  installed at the distal end of the endoscope  112  in the first embodiment which is unnecessary in the second embodiment. Hence, the differences from the first embodiment will be described. 
     As mentioned above, the endoscope  112  of  FIG. 6  is the same as the endoscope  12  of the first embodiment except that the fluorescent body  24  is not present at the distal end of the endoscope. Hence, an optical fiber  112  is the same as the optical fiber  22 , an irradiation port  128 A is the same as the irradiation port  28 A, a light-receiving part  128 B is the same as the light-receiving part  28 B, an imaging element  126  is the same as the imaging element  26 , and a scope cable  130  is the same as the scope cable  30 , and these components perform the same operations, respectively. 
     Additionally, as shown in  FIG. 6 , a light source device  114  includes a broadband light source  132 , a light quantity diaphragm  133 , a filter set  134  including a first color filter  134 B and a second color filter  134 G, and a condensing lens  135 . Additionally, the light source device  114  forms a first light source section by the combination of the broadband light source  132  and the first color filter  134 B, and forms a second light source section by the combination of the broadband light source  132  and the second color filter  134 G. The broadband light source  132  is, for example, a xenon light source which irradiates xenon light, for example, and irradiates predetermined broadband light (white light). 
     Additionally, the broadband light source  132  performs light quantity adjustment using the light quantity diaphragm  133 . Since adjustment of the emission intensity of the broadband light source  132  is difficult unlike the laser light source in the first embodiment, light quantity is adjusted by the light quantity diaphragm. Accordingly, the emission intensity of the broadband light source  132  is constant in principle. 
     In addition, in the present embodiment, xenon light is used as the broadband light, and a xenon light source is used as the broadband light source  132 . However, in the invention, the light source is not particularly limited if a light source which irradiates white illumination light capable of being band-narrowed using the first color filter and the second color filter is adopted. In addition to the xenon light source, discharge tubes including discharge-type high-luminance lamp light sources, such as a mercury lamp or a metal halide lamp, can be used. 
     Additionally, a white light source in which a laser light source and a fluorescent body are combined together can also be used. In this case, since the emission intensity can be adjusted depending on the driving current value of the laser light source unlike the above description, the light quantity diaphragm  133  is unnecessary. 
     After irradiated broadband light is turned into a substantially parallel pencil by a reflector (not shown) which is a convergence optical system and the light quantity thereof is adjusted by the light quantity diaphragm  133 , the light is transmitted through a predetermined filter of the filter set  134 . 
     The narrow-banded light which is transmitted through the first color filter  134 B and the second color filter  134 G is condensed at an incidence end of the optical fiber  112  by the condensing lens  135 , and enters the optical fiber  112 . The entered light is guided by the optical fiber  112  and irradiated from the distal end of the endoscope. 
     The broadband light transmitted through the first color filter  134 B is irradiated from the distal end of the endoscope as the first narrowband light, and the broadband light transmitted through the second color filter  134 B is emitted from the distal end of the endoscope as the second narrowband light. 
     The filter set  134 , as shown in  FIG. 7 , is made up of the first color filter  134 B which converts broadband light into blue narrowband light (B light or first narrowband light), the second color filter  134 G which converts broadband light into green narrowband light (G light or second narrowband light), and a transmission part  134 T which allows broadband light to be transmitted therethrough as it is. Additionally, the first color filter  134 B is made up of a blue filter  134 B 1  with a narrow half-value width, and a blue filter  134 B 2  with a wide half-value width, and the second color filter  134 G is made up of a green filter  134 G 1  with a narrow half-value width, and a green filter  134 G 2  with a wide half-value width. The filter set  134  is switched by a moving unit and a rotating unit (not shown) according to an instruction from a light source control unit  148  (refer to  FIG. 9 ). 
       FIG. 8A  is a graph showing an example of the spectral characteristics of the blue filter  134 B 1  with a narrow half-value width and the green filter  134 G 1  with a narrow half-value width, and  FIG. 8B  is a graph showing an example of the spectral characteristics of the blue filter  134 B 2  with a wide half-value width, and the green filter  134 G 2  with a wide half-value width. 
     When the light quantity is insufficient even if the light quantity diaphragm  133  is opened to the maximum, thereby maximizing the irradiation light quantity, the irradiation light quantity can be further increased by performing switching from the filter with a narrow half-value width to the filter with a wide half-value width as mentioned above. 
       FIG. 9  is a block diagram showing signal processing systems of respective sections including the detailed configuration of the processor of the second embodiment of the endoscope apparatus of the invention. The difference from  FIG. 3  of the first embodiment shown in  FIG. 3  is the light source device  114 . In addition, since the difference between the endoscope  112  and the endoscope  12  is only the fluorescent body  24 , there is no constitutional difference in the block diagram showing the signal processing system of  FIG. 9 . 
     Accordingly, similarly to the above description, the light source device  114  which is the difference from the first embodiment will be described. 
     The signal processing system of the light source device  114  has the light source control unit  148  which performs ON/OFF control of the broadband light source  132 , light quantity control using the light quantity diaphragm  133 , switching control from the filters  134 B 1  and  134 G 1  with a narrow half-value width to the filters  134 B 2  and  134 G 2  with a wide half-value width using the moving unit (not shown), and switching control of the first color filter  134 B, the second color filter  134 G, and the transmission part  134 T using the rotating unit (not shown). 
     Here, the light source control unit  148  turns on the broadband light source  132  according to a light source ON signal accompanying the starting-up of the endoscope apparatus  10 , the controls switching between the transmission part  134 T, and the first color filter  134 B and the second color filter  134 G of the filter set  134  according to a switching signal between the normal light mode and the special light mode from the mode switching section  40 , controls the light quantity of broadband light, that is, the light quantity diaphragm  133  through the light source control unit  148 , using the light source light quantity changing unit  55 , thereby controlling the irradiation light quantity from the broadband light source  132 , so that the luminance values of the aforementioned captured image signals become predetermined luminance values according to the luminance values of captured image information calculated from the luminance value calculating unit  50 , and performs switching of the filter set  134  from the filters  134 B 1  and  134 G 1  with a narrow half-value width to the filters  134 B 2  and  134 G 2  with a wide half-value width, thereby controlling the irradiation light quantities thereof. 
     The light source light quantity changing unit  55  switches the blue filter  134 B 1  with a narrow half-value width and the green filter  134 G 1  with a narrow half-value width in the first color filter  134 B and the second color filter  134 G to the blue filter  134 B 2  with a wide half-value width and the green filter  134 G 2  with a wide half-value width, on the basis of the information on the light quantity diaphragm  133  using the light source control unit  148 , the information on installed filters of the filter set  134 , and the calculated luminance values. Here, the installed filters mean filters which allow broadband light to be transmitted therethrough in practice. Additionally, the information on the installed filters is information on whether any filters of the aforementioned filters  134 B 1 ,  134 B 2 ,  134 G 1 , and  134 G 2 , and the transmission part  134 T are selected as the installed filters. 
     For example, when there is no need to raise the luminance values of a captured image and the irradiation light quantities are sufficient, it is not necessary to raise the irradiation light quantities to a fixed value or more. Therefore, the filters  134 B 1  and  134 G 1  with a narrow half-value width are sufficient. When it is necessary to raise the luminance values of a captured image and it is necessary to raise the irradiation light quantities to a fixed value or more, there is a limit to the light quantities which can be transmitted through a filter with a narrow half-value width. Therefore, an instruction for switching of the first color filter  134 B and the second color filter  134 G is issued to the light source control unit  148  so that switching to the filters  134 B 2  and  134 G 2  with a wide half-value width from the filters  134 B 1  and  134 G 1  with a narrow half-value width is performed. Thereby, the luminance values of a captured image become predetermined luminance values suitable for observation. In addition, the aforementioned fixed value means the irradiation light quantity when the light quantity diaphragm  133  is maximized using the filters  134 B 1  and  134 G 1  with a narrow half-value width as the installed filters. 
     Additionally, the information on the light quantity diaphragm  133  of the broadband light source  132  in the light source light quantity changing unit  55  and the information on the installed filters of the filter set  134  are also output to the white balance adjustment value calculating unit  57 . 
     The light source control unit  148  controls the light quantity diaphragm  133  on the basis of the information on the aforementioned luminance values, and an instruction from the light source light quantity changing unit  55 , thereby controlling the irradiation light quantity from the broadband light source  132 , and switches the installed filters from the filters B1 and G1 with a narrow half-value width of the filter set  134  to the filter B2 and G2 with a wide half-value width, thereby controlling the irradiation light quantities. 
     On the basis of the irradiation light quantity of broadband light in the light source light quantity changing unit  55 , and the information on the installed filters of the filter set  134 , the white balance adjustment value calculating unit  57  calculates the white balances when imaging is performed with illumination light, and calculates, as white balance gains, white balance adjustment values required in order to adopt the white balances when imaging is performed with illumination light, as basis white balances. 
     Depending on whether broadband light has been transmitted through any filter of the blue filter  134 B 1  with a narrow half-value width, the blue filter  134 B 2  with a wide half-value width, the green filter  134 G 1  with a narrow half-value width, and the green filter  134 G 2  with a wide half-value width, the wavelength profile of the narrowband light after the transmission is determined as shown in  FIGS. 8A and 8B . 
     Hence, it turns out that the white balances are uniquely determined in advance depending on the irradiation light quantities of the broadband light which is transmitted through the aforementioned filters  134 B 1 ,  134 B 2 ,  134 G 1 , and  134 G 2 . 
     The white balance adjustment value calculating unit  57  of  FIG. 9  includes a white balance table (not shown) recorded by measuring the relationship between irradiation light quantity and white balance with respect to the type of installed filters in advance, and calculates the white balances of captured image information, using the white balance table from the information on the irradiation light quantity of the broadband light output from the light quantity changing unit  55  and the information on the installed filters. 
     Additionally, as for the basis white balances, the white balances of a captured image when imaging is performed using the filters B1 and G1 with a narrow half-value width may be adopted as the basis white balances. 
     The reason why the white balances have collapsed is that the filters B2 and G2 with a wide half-value width are used since light quantity is insufficient, and that there is no necessity for gain adjustment when light quantity is sufficient if the white balances of a captured image when captured image information is acquired using the filters B1 and G1 with a narrow half-value width as the installed filters are adopted as the basis white balances. 
     The white balance adjustment value calculating unit  57  calculates white balance gains as white balance adjustment values for adjusting the calculated white balances to the basis white balances, and outputs the gains to the gain adjusting unit  59 . 
     When imaging is performed using the filters B2 and G2 with a wide half-value width as the installed filters, as mentioned above, the gain adjusting unit  59  is used in order to adjust the white balances of captured image signals to the white balances when the filters B1 and G2 with a narrow half-value width are used as the installed filters. 
     In the gain adjusting unit  59 , a B image signal including a B light image component and a G image signal including a G light image component in which the white balances of the captured image signals are adjusted are output to the special light image processing section  64 , respectively, and are synthesized into one image data. Specifically, the synthesis of the image data is performed by allocating the G image signal to R image data, and allocating the B image signal to B image data and G image data similarly to the image processing performed in the aforementioned special light image processing section  64 . The processing except for synthesizing one item of image data from the B image signal and G image signal imaged in two frames is the same as that of the first embodiment. 
     In addition, in the second embodiment, in the special light color conversion section  74 , the irradiation light quantity from the broadband light source  132  and the information on the installed filters are used instead of the information on the changed irradiation light quantities and light quantity ratios that are used in the first embodiment. This is because the light quantity ratios in the first embodiment, that is, the ratio between R light component, G light component, and B light component of illumination light can be calculated depending on the information on the irradiation light quantities and the installed filters. 
     The configuration other than the above description is the same as that of the first embodiment. The second embodiment of the endoscope apparatus of the invention is basically configured as described above. 
     Next, the operation of the second embodiment of the endoscope apparatus  110  of the invention will be described with reference to the flowchart of  FIG. 10 . The description of the same operation as in the first embodiment is omitted partially, and differences will be mainly described. 
     Even in the present embodiment, first, normal light observation shall be performed in the normal light mode. That is, the transmission part  134 T is installed as the installed filter, the broadband light source is turned on, and normal light image processing is performed on captured image data based on broadband light in the normal light image processing section  64 . 
     Here, switching to the special light mode is performed by a user according to the steps shown in  FIG. 10  (S 110 ). The second embodiment adopts the face sequential system which images B image data and G image data in two frames in the special light imaging in terms of the configuration thereof. 
     If switching to the special light mode is made, first, the blue filter  134 B 1  with a narrow half-value width is installed as the installed filter in a first frame. Then, broadband light is emitted from the broadband light source  132 , and the irradiation light quantity thereof is adjusted by the light quantity diaphragm  133 , whereby a predetermined light quantity of broadband light is turned into the first narrowband light through the blue filter  134 B 1  with a narrow half-value width, and is irradiated toward an object from the distal end of the endoscope (S 112 ). 
     The irradiated first narrowband light is reflected by the object, the return light is acquired by the imaging element  126  as captured image signals (captured image information), and the luminance values of the captured image signals acquired by the imaging element  126  are calculated in the luminance value calculating unit  50 . The luminance values of the calculated captured image signals are output to the light source light quantity changing unit  55  and the light source control unit  148  (S 114 ). 
     Then, the light source light quantity changing unit  55  adjusts the light quantity of the light quantity diaphragm  133  to change the irradiation light quantity of the broadband light source  132  so that the captured image is not too bright and is not too dark and the luminance values become predetermined luminance values, on the basis of the information on the luminance values calculated in the luminance value calculating unit  50 , the information on the light quantity of broadband light controlled from the light source control unit  148 , that is, the information of the light quantity diaphragm  133  and the information of the installed filters, and changes the installed filters from the filters with a narrow half-value width to the filters with a wide half-value width to change the irradiation light quantities when the irradiation light quantities are insufficient. Then, the information on the changed irradiation light quantities and installed filters is output to the light source control unit  148  and the white balance adjustment value calculating unit  57 , respectively (S 116 ). 
     Since Step S 114  and Step S 116  are performed according to changes in the luminance values, these steps are performed according to a change in the positional relationship between the distal end of the endoscope and the object. 
     Additionally, the white balance adjustment value calculating unit  57  calculates the white balances of the captured image on the basis of the information on the aforementioned changed irradiation light quantities and installed filters. The white balances is calculated on the basis of the irradiation light quantity of broadband light, the information on the installed filters, and the white balance table (not shown) as mentioned above (S 118 ). 
     Then, white balance gains required in order to maintain the white balances are calculated from the calculated white balances and the basis white balances, and the white balance gains are adjusted in the CDS•AGC circuit  44  through the gain adjusting unit  59  (S 120 ). 
     After the irradiation light quantity from the broadband light source  132  and the installed filters are changed by the light source light quantity changing unit  55 , and the white balance gains are adjusted by the gain adjusting unit  59 , imaging of an object is performed and a captured image signal (B image signal) of the first frame is acquired by the imaging element  26  (S 122 ). The acquired B image signal is temporarily stored in the special light image processing section  64 . 
     Next, in the second frame, the installed filter is switched to the green filter  134 G 1  with a narrow half-value width (S 124 ). 
     If the installed filter is switched, previous steps S 114  to S 124  are repeatedly performed, and a captured image signal (G image signal) of the second frame is acquired (S 126 ). The acquired G image signal is stored in the special light image processing section  64  similarly to the first frame. 
     The B image signal and the G image signal which are temporarily stored in the special light image processing section  64  are synthesized into one item of RGB image data. Similarly to Step S 24 , the RGB image data is synthesized by allocating the G image signal to R image data, and allocating the B image signal to B image data and G image data. The RGB image data is subjected to various processing similarly to Step S 24 , and is output to the image display signal generating section  66  (S 128 ). 
     Similarly to Step S 26 , the RGB image data output to the image display signal generating section  66  is converted into image display signals which can be displayed, is displayed on the monitor  38  as a special light image, and is recorded in the recording device  42  (S 130 ). 
     In this way, an image component of B light and an image component of G light which are white-balanced can be acquired, respectively, as the first frame and the second frame are alternately repeated. A special light captured image is obtained by synthesizing the image component of B light and the image component of G light which are imaged in this way in the special light image processing section  64 . 
     The above is the second embodiment of the invention. 
     Although the endoscope apparatus of the invention has been described in detail above, the invention is not limited to the above embodiments, and various improvements and modifications may be performed without departing from the scope of the invention.