Patent Publication Number: US-8994804-B2

Title: Scanning endoscope system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of PCT/JP2013/062916 filed on May 8, 2013 and claims benefit of Japanese Application No. 2012-193339 filed in Japan on Sep. 3, 2012, the entire contents of which are incorporated herein by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a scanning endoscope system, and more particularly to a scanning endoscope system that acquires an image by scanning an object. 
     2. Description of the Related Art 
     Various kinds of techniques for reducing a size of an insertion portion to be inserted into a body cavity of a subject are proposed for endoscopes in the medical fields, in order to alleviate a burden on the subject. As one example of such techniques, a scanning endoscope which does not include a solid-state image pickup device at the part corresponding to the above-described insertion portion, and a system provided with the scanning endoscope are known. 
     Specifically, the system including the above-described scanning endoscope is configured, for example, to scan an object in a preset scanning pattern by causing the distal end portion of the illumination fibers for guiding illumination light emitted from the light source section to swing, receive return light from the object with the light-receiving fibers arranged around the illumination fibers, and generate an image of the object using a signal obtained by separating the return light received with the light-receiving fibers into color components. 
     As a calibration method applicable to the system including the above-described configuration, the calibration method disclosed in Japanese Unexamined Patent Application Publication No. 2010-515947 has been conventionally known, for example. Specifically, Japanese Unexamined Patent Application Publication No. 2010-515947 discloses the calibration method of acquiring a multi-colored image in the multi-colored calibration pattern using a scanning beam device, comparing the respective color components of the acquired multi-colored image with the display color components of the multi-colored calibration pattern, which correspond to the respective color components, and calibrates the scanning beam device based on the result of the comparison. 
     In addition, in a common image pickup apparatus and the like, a color balance adjustment has been conventionally performed for bringing the color of the object included in an image close to the natural color when the object is seen with the naked eye, for example. 
     SUMMARY OF THE INVENTION 
     A scanning endoscope system according to one aspect of the present invention includes: a scanning endoscope including a light-guiding section that guides illumination light emitted from a light source, a driving section that enables the light-guiding section to swing such that an irradiation position of the illumination light emitted to an object through the light-guiding section draws a trajectory corresponding to a predetermined scanning pattern, and a light-receiving section that receives return light of the illumination light emitted to the object; a test chart device comprising a plane portion including a first region and a second region; a light detection section configured to generate a signal corresponding to an intensity of the return light received at the light-receiving section and output the generated signal; a pixel generation section configured to generate sampling pixels on the predetermined scanning pattern by sampling the signal outputted from the light detection section in a given sampling cycle; a first correction value calculation section configured to extract the first region from an image of the plane portion which includes the respective sampling pixels generated by the pixel generation section, and to further calculate a first correction value to be used for color balance adjustment of an image of the object based on a pixel value of each of the sampling pixels included in the first region; and a second correction value calculation section configured to extract the second region from the image of the plane portion which includes the respective sampling pixels generated by the pixel generation section, and to further calculate a second correction value to be used for pixel shift correction of the image of the object based on a pixel position of each of the sampling pixels included in the second region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a configuration of a main part of a scanning endoscope system according to an embodiment. 
         FIG. 2  illustrates an example of a virtual XY plane set on a surface of an object. 
         FIG. 3  illustrates an example of a signal waveform of a first driving signal supplied to an actuator provided in an endoscope. 
         FIG. 4  illustrates an example of a signal waveform of a second driving signal supplied to the actuator provided in the endoscope. 
         FIG. 5A  illustrates a temporal displacement of an irradiation coordinate of illumination light from a point SA to reach a point YMAX in the case where the virtual XY plane as shown in  FIG. 2  is irradiated with the illumination light. 
         FIG. 5B  illustrates a temporal displacement of the irradiation coordinate of illumination light from the point YMAX to reach the point SA in the case where the virtual XY plane as shown in  FIG. 2  is irradiated with the illumination light. 
         FIG. 6  illustrates a configuration of a test chart device used together with the scanning endoscope system according to the embodiment. 
         FIG. 7  illustrates an example of a configuration of a bottom surface portion of the test chart device. 
         FIG. 8  is a flowchart showing an example of processing and the like performed in the scanning endoscope system according to the embodiment. 
         FIG. 9  schematically illustrates how to divide into a group GR1 and a group GR2 in processing related to a calculation of pixel shift correction values. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, an embodiment of the present invention will be described with reference to drawings. 
       FIGS. 1 to 9  relate to the embodiment of the present invention.  FIG. 1  illustrates a configuration of a main part of a scanning endoscope system according to the embodiment. 
     A scanning endoscope system  1  includes a scanning endoscope  2  to be inserted into a body cavity of a subject, a main body apparatus  3  connected to the scanning endoscope  2 , and a monitor  4  connected to the main body apparatus  3 , as shown in  FIG. 1 , for example. 
     The scanning endoscope  2  includes an insertion portion  11  formed in an elongated shape and having flexibility so as to be insertable into the body cavity of the subject. The insertion portion  11  includes at the proximal end portion thereof a connector and the like, not shown, for detachably connecting the scanning endoscope  2  to the main body apparatus  3 . 
     Illumination fibers  12  having a function as a light-guiding section that guides the illumination light supplied from a light source unit  21  of the main body apparatus  3  to an objective optical system  14  and light-receiving fibers  13  that receive return light from the object to guide the received light to a detection unit  23  of the main body apparatus  3  are respectively inserted through a part from the proximal end portion to the distal end portion inside the insertion portion  11 . 
     An end portion including a light incident surface of the illumination fibers  12  is arranged at a multiplexer  32  provided in the main body apparatus  3 . In addition, an end portion including a light exit surface of the illumination fibers  12  is arranged in the vicinity of a light incident surface of a lens  14   a  provided at the distal end portion of the insertion portion  11  in a state where the end portion is not fixed with a fixing member or the like. 
     An end portion including a light incident surface of the light-receiving fibers  13  is fixedly arranged around the light exit surface of the lens  14   b  on the distal end surface of the distal end portion of the insertion portion  11 . In addition, an end portion including the light exit surface of the light-receiving fibers  13  is arranged at a demultiplexer  36  provided in the main body apparatus  3 . 
     The objective optical system  14  includes the lens  14   a  on which the illumination light from the illumination fibers  12  is incident, and a lens  14   b  that emits the illumination light passed through the lens  14   a  to the object. 
     At the halfway portion of the illumination fibers  12 , which is located on the distal end portion side of the insertion portion  11 , an actuator  15  that drives based on a driving signal outputted from a driver unit  22  of the main body apparatus  3  is attached. 
     Hereinafter, description will be made by taking the case where the XY plane as shown in  FIG. 2  is set on the surface of the object as a virtual plane perpendicular to the insertion axis (or the optical axis of the objective optical system  14 ) corresponding to the axis in the longitudinal direction of the insertion portion  11 , as an example.  FIG. 2  illustrates an example of the virtual XY plane set on the surface of the object. 
     Specifically, the point SA on the XY plane in  FIG. 2  shows an intersection of the insertion axis and the paper surface based on a virtual setting in which the insertion axis of the insertion portion  11  is supposed to exist in the direction from the near side to the far side of the paper surface. The X-axis direction on the XY plane in  FIG. 2  is set as the direction from the left side toward the right side of the paper surface. The Y-axis direction on the XY plane in  FIG. 2  is set as the direction from the down side toward the up side of the paper surface. The X-axis and the Y-axis which constitute the XY plane in  FIG. 2  intersect with each other at the point SA. 
     The actuator  15  includes an X-axis actuator (not shown) that operates so as to cause the end portion including the light exit surface of the illumination fibers  12  to swing in the X-axis direction on the basis of a first driving signal outputted from the driver unit  22  of the main body apparatus  3 , and the Y-axis actuator (not shown) that operates so as to cause the end portion including the light exit surface of the illumination fibers  12  to swing in the Y-axis direction on the basis of a second driving signal outputted from the driver unit  22  of the main body apparatus  3 . The end portion including the light exit surface of the illumination fibers  12  is spirally swung with the point SA as the center in accordance with the operations of the X-axis actuator and the Y-axis actuator as described above. 
     The insertion portion  11  includes inside thereof a memory  16  in which endoscope information including various kinds of information such as individual discrimination information of the scanning endoscope  2  are stored in advance. The endoscope information stored in the memory  16  is read by the controller  25  when the scanning endoscope  2  is connected to the main body apparatus  3 . 
     On the other hand, the main body apparatus  3  includes the light source unit  21 , the driver unit  22 , the detection unit  23 , a memory  24 , and the controller  25 . 
     The light source unit  21  includes light sources  31   a ,  31   b , and  31   c , and the multiplexer  32 . 
     The light source  31   a  includes a laser light source, or the like, for example, and emits light in a red wavelength band (hereinafter, referred also as R light) to the multiplexer  32  when being turned on under the control by the controller  25 . 
     The light source  31   b  includes a laser light source, or the like, for example, and emits light in a green wavelength band (hereinafter also referred to as G light) to the multiplexer  32  when being turned on under the control by the controller  25 . 
     The light source  31   c  includes a laser light source, or the like, for example, and emits light in a blue wavelength band (hereinafter also referred to as B light) to the multiplexer  32  when being turned on under the control by the controller  25 . 
     The multiplexer  32  is configured to be able to multiplex the R light emitted from the light source  31   a , the G light emitted from the light source  31   b , and the B light emitted from the light source  31   c , to supply the multiplexed light to the light incident surface of the illumination fibers  12 . 
     The driver unit  22  includes a signal generator  33 , digital/analog (hereinafter referred to as D/A) converters  34   a ,  34   b , and an amplifier  35 . 
     The signal generator  33  generates a signal of a predetermined waveform as shown in  FIG. 3 , for example, as the first driving signal for causing the end portion including the light exit surface of the illumination fibers  12  to swing in the X-axis direction, to output the generated signal to the D/A converter  34   a , based on the control by the controller  25 .  FIG. 3  illustrates an example of the signal waveform of the first driving signal supplied to the actuator provided in the scanning endoscope. 
     In addition, the signal generator  33  generates a signal of a waveform whose phase is shifted by 90 degrees from the phase of the waveform of the above-described first driving signal, as shown in  FIG. 4 , for example, as the second driving signal for causing the end portion including the light exit surface of the illumination fibers  12  to swing in the Y-axis direction, to output the generated signal to the D/A converter  34   b , based on the control by the controller  25 .  FIG. 4  illustrates an example of the signal waveform of the second driving signal supplied to the actuator provided in the scanning endoscope. 
     The D/A converter  34   a  converts the first driving signal in the digital form outputted from the signal generator  33  into the first driving signal in the analog form, to output the converted driving signal to the amplifier  35 . 
     The D/A converter  34   b  converts the second driving signal in the digital form outputted from the signal generator  33  into the second driving signal in the analog form, to output the converted signal to the amplifier  35 . 
     The amplifier  35  amplifies the first and second driving signals respectively outputted from the D/A converters  34   a  and  34   b , to output the amplified driving signals to the actuator  15 . 
     The amplitude value (signal level) of the first driving signal exemplified in  FIG. 3  gradually increases with the time T1 at which the amplitude value is minimum value, as a starting point, then gradually decreases after reaching the maximum value at the time T2, and becomes the minimum value again at the time T3. 
     In addition, the amplitude value (signal level) of the second driving signal exemplified in  FIG. 4  gradually increases at the time T1 at which the amplitude value is minimum value, as a starting point, then gradually decreases after reaching the maximum value around the time T2, and becomes the minimum value again at the time T3. 
     When the first driving signal as shown in  FIG. 3  is supplied to the X-axis actuator of the actuator  15  and the second driving signal as shown in  FIG. 4  is supplied to the Y-axis actuator of the actuator  15 , the end portion including the light exit surface of the illumination fibers  12  is swung in a spiral shape with the point SA as the center, and in accordance with such a swing, the surface of the object is scanned in the spiral shapes as shown in  FIGS. 5A and 5B .  FIG. 5A  illustrates a temporal displacement of an irradiation coordinate of the illumination light from the point SA to reach the point YMAX in the case where the virtual XY plane as shown in  FIG. 2  is irradiated with the illumination light.  FIG. 5B  illustrates a temporal displacement of the irradiation coordinate of the illumination light from the point YMAX to reach the point SA in the case where the virtual XY plane as shown in  FIG. 2  is irradiated with the illumination light. 
     Specifically, the position corresponding to the point SA on the surface of the object is irradiated with the illumination light at the time T1. After that, in accordance with the increase in the amplitude values of the first and second driving signals from the time T1 to the time T2, the irradiation coordinate of the illumination light on the surface of the object displaces so as to draw a first spiral-shaped trajectory toward outside with the point SA as the starting point, and when the time reaches the time T2, the point YMAX, which is the outmost point of the irradiation coordinate of the illumination light on the surface of the object, is irradiated with the illumination light. Then, in accordance with the decrease in the amplitude values of the first and second driving signals from the time T2 to the time T3, the irradiation coordinate of the illumination light on the surface of the object displaces so as to draw a second spiral-shaped trajectory toward inside with the point YMAX as the starting point, and when the time reaches the time T3, the point SA on the surface of the object is irradiated with the illumination light. 
     That is, the actuator  15  is capable of causing the end portion including the light exit surface of the illumination fibers  12  to swing such that the irradiation position of the illumination light emitted through the objective optical system  14  to the object draws the trajectory corresponding to each of the spiral-shaped scanning patterns as illustrated in  FIG. 5A  and  FIG. 5B , based on the first and second driving signals supplied from the driver unit  22 . 
     The detection unit  23  includes the demultiplexer  36 , the detectors  37   a ,  37   b , and  37   c , and analog/digital (hereinafter referred to as A/D) converters  38   a ,  38   b , and  38   c.    
     The demultiplexer  36  includes a dichroic mirror, etc., and separates the return light emitted from the light exit surface of the light-receiving fibers  13  into light of each of the color components of R (red), G (green), and B (blue), to emit the light subjected to the separation to the detectors  37   a ,  37   b , and  37   c.    
     The detector  37   a  detects the intensity of the R light outputted from the demultiplexer  36  and generates an analog R signal corresponding to the detected intensity of the R light, to output the generated analog R signal to the A/D converter  38   a.    
     The detector  37   b  detects the intensity of the G light outputted from the demultiplexer  36 , and generates an analog G signal corresponding to the detected intensity of the G light, to output the generated analog G signal to the A/D converter  38   b.    
     The detector  37   c  detects the intensity of the B light outputted from the demultiplexer  36 , and generates an analog B signal corresponding to the detected intensity of the B light, to output the generated analog B signal to the A/D converter  38   c.    
     The A/D converter  38   a  converts the analog R signal outputted from the detector  37   a  into a digital R signal, to output the digital R signal to the controller  25 . 
     The A/D converter  38   b  converts the analog G signal outputted from the detector  37   b  into a digital G signal, to output the digital G signal to the controller  25 . 
     The A/D converter  38   c  converts the analog B signal outputted from the detector  37   c  into a digital B signal, to output the digital B signal to the controller  25 . 
     The memory  24  stores, in advance, a control program for controlling the main body apparatus  3  and the like. In addition, the memory  24  stores a mapping table MPT1 including information related to the coordinate position (pixel position) of each of sampling pixels sampled in a given sampling cycle SC when the illumination light is emitted (in a period corresponding to the time T1 to the time T2) along the scanning pattern in the ideal spiral shape as shown in  FIG. 5A , and a mapping table MPT2 including information related to the coordinate position (pixel position) of each of sampling pixels sampled in the given sampling cycle SC when the illumination light is emitted (in a period corresponding to the time T2 to the time T3) along the scanning pattern in the ideal spiral shape as shown in  FIG. 5B . 
     The controller  25  includes a CPU, etc., and is configured to read the control program stored in the memory  24  and control the light source unit  21  and the driver unit  22  based on the read control program. 
     In a case where the controller  25  detects that the endoscope information read from the memory  16  when the insertion portion  11  is connected to the main body apparatus  3  is not stored (saved) in the memory  24 , the controller  25  stores (saves) the read endoscope information into the memory  24 . 
     The controller  25  acquires a white balance correction value to be used in white balance adjustment processing, based on the R signal, the G signal, and the B signal outputted from the detection unit  23  in accordance with the return light received when a bottom surface portion  102  of a test chart device  101  to be described later is irradiated with the illumination light, to store the acquired white balance correction value into the memory  24 . 
     The controller  25  acquires a pixel shift correction value to be used in pixel shift correction processing, based on the R signal, the G signal, and the B signal outputted from the detection unit  23  in accordance with the return light received when the bottom surface portion  102  of the test chart device  101  to be described later is irradiated with the illumination light, to write the acquired pixel shift correction value into the mapping table MPT1 or MPT2 in the memory  24 . 
     The controller  25  includes a function as a pixel generation section and is capable of generating sampling pixels by sampling the R signal, the G signal, and the B signal outputted from the detection unit  23  in the given sampling cycle SC in a period corresponding to the time T1 to the time T2, generating interpolation pixels by performing interpolation processing based on the sampling pixels, and further generating an image for one frame based on the sampling pixels and the interpolation pixels. In addition, the controller  25  is capable of respectively performing the white balance adjustment processing based on white balance correction values stored in the memory  24  and the pixel shift correction processing based on pixel shift correction values written into the mapping table MPT1 stored in the memory  24 , on the image for one frame (in the period corresponding to the time T1 to the time T2) generated as described above. 
     The controller  25  includes the function as the pixel generation section and is capable of generating sampling pixels by sampling the R signal, the G signal, and the B signal outputted from the detection unit  23  in the given sampling cycle SC in a period corresponding to the time T2 to the time T3, generating interpolation pixels by performing interpolation processing based on the sampling pixels, and further generating an image for one frame based on the sampling pixels and the interpolation pixels. In addition, the controller  25  is capable of respectively performing the white balance adjustment processing based on white balance correction values stored in the memory  24  and the pixel shift correction processing based on pixel shift correction values written into the mapping table MPT2 stored in the memory  24 , on the image for one frame (in the period corresponding to the time T2 to the time T3) generated as described above. 
     The controller  25  causes the image subjected to the white balance adjustment processing and the pixel shift correction processing to be displayed on the monitor  4 . 
     Description will be made on the configuration of the test chart device  101  used for acquiring the above-described white balance correction values and the pixel shift correction values.  FIG. 6  illustrates the configuration of the test chart device used together with the scanning endoscope system according to the embodiment.  FIG. 7  illustrates an example of the configuration of the bottom surface portion of the test chart device. 
     As shown in  FIG. 6 , the test chart device  101  is formed as a bottomed cylinder body that allows the distal end portion of the insertion portion  11  to be inserted from an opening portion into an internal space of the cylinder body. In addition, as shown in  FIGS. 6 and 7 , the test chart device  101  has the bottom surface portion  102  as a plane portion provided inside the bottomed cylinder body, a white inner circumferential side surface portion  103 , and a positioning member  104 . The bottom surface portion  102  includes a region for white balance adjustment  102   a  and a region for pixel shift correction  102   b.    
     The region for white balance adjustment  102   a  is configured as a solid white region provided at a peripheral portion of the bottom surface portion  102 . 
     The region for pixel shift correction  102   b  is configured as a region with a lattice pattern which is provided (drawn) at the center of the bottom surface portion  102 . 
     The respective segments in a vertical direction (corresponding to the Y-axis direction on the virtual XY plane shown in  FIG. 2 ) included in the lattice pattern of the region for pixel shift correction  102   b  are drawn in a first color (red, for example) of red, green, and blue. The respective segments in a horizontal direction (corresponding to the X-axis direction on the virtual XY plane shown in  FIG. 2 ) included in the lattice pattern of the region for pixel shift correction  102   b , are drawn in a second color (green, for example) of red, green, and blue, which is different from the first color. Furthermore, the respective segments in the vertical direction and the horizontal direction included in the lattice pattern of the region for pixel shift correction  102   b  are drawn so as to be apart from each other by the fixed and the same space equal to or larger than the size of one pixel. The shape of the region for pixel shift correction  102   b  is not limited to the square shown in  FIG. 2 , but may be any shape of rectangle, circle, ellipse, and polygon, for example. 
     The positioning member  104  is formed as a cylindrical body (or tubular body) with a flange, as shown in  FIG. 6 , for example. 
     Specifically, the positioning member  104  has a shape that allows the distal end portion of the insertion potion  11  to be fixedly arranged at a position where the distal end surface of the insertion potion  11  and the bottom surface portion  102  face each other, with the distance between the distal end surface and the bottom surface portion  102  being maintained at a predetermined distance, when the insertion portion  11  is inserted into the internal space of the test chart device  101 . Furthermore, the positioning member  104  includes a hole of such a diameter as not to shield the illumination light emitted through the objective optical system  14  in the state where the distal end portion of the insertion portion  11  is fixedly arranged at the above-described position. 
     Next, description will be made on the working, etc., of the scanning endoscope system  1  configured as described above. Hereinafter, description will be mainly made on the case where the endoscope information read from the memory  16  of the scanning endoscope  2  is not stored (saved) in the memory  24 . 
     First, an operator or the like connects the scanning endoscope  2  and the monitor  4  respectively to the main body apparatus  3 , and then inserts the scanning endoscope  2  from the opening portion into the internal space of the test chart device  101 , to thereby arrange the distal end portion of the insertion portion  11  at the position where the distal end surface of the insertion portion  11  and the bottom surface portion  102  face each other, the distance between the distal end surface of the insertion portion  11  and the bottom surface portion  102  is maintained at a predetermined distance, and the optical axis of the objective optical system  14  coincides with the center of the lattice pattern of the region for pixel shift correction  102   b . Such an arrangement allows the point SA on the virtual XY plane shown in  FIG. 2  to coincide with the center of the lattice pattern of the region for pixel shift correction  102   b.    
     When power sources of the respective sections in the scanning endoscope system  1  are turned on, the endoscope information stored in the memory  16  of the insertion portion  11  is read by the controller  25 , and the read endoscope information is stored in the memory  24 . 
     The controller  25  controls the light source unit  21  to switch the light sources  31   a ,  31   b , and  31   c  from off to on and controls the driver unit  22  to cause the first and second driving signals to be outputted to the actuator  15 , at a timing immediately after the endoscope information read from the memory  16  is stored in the memory  24 . With such controls performed by the controller  25 , the surface of the bottom surface portion  102  is irradiated with the white light obtained by mixing the R light, the G light, and the B light, which is the illumination light, the return light from the bottom surface portion  102  is received with the light-receiving fibers  13 , and the R signal, the G signal, and the B signal corresponding to the return light received by the light-receiving fibers  13  are outputted from the detection unit  23 . 
     After that, when the controller  25  detects that a calibration switch (not shown) provided on the main body apparatus  3  is pressed, for example, the controller  25  acquires the white balance correction values and the pixel shift correction values by performing the processing as described below. 
     Now, description will be made on the processing related to the acquisition of the white balance correction values and the pixel shift correction values.  FIG. 8  is a flowchart showing one example of processing and the like performed in the scanning endoscope system according to the embodiment. 
     The controller  25  generates the sampling pixels by sampling the R signal, the G signal, and the B signal outputted from the detection unit  23  in the given sampling cycle SC, generates the interpolation pixels by performing interpolation processing based on the sampling pixels, further generates an image of the bottom surface portion  102  based on the generated sampling pixels and interpolation pixels, and then extracts a region corresponding to the region for white balance adjustment  102   a  from the generated image of the bottom surface portion  102  (step S 1  in  FIG. 8 ). 
     The controller  25  calculates the white balance correction values based on the pixel values of the respective sampling pixels included in the region for white balance adjustment  102   a  extracted in the step S 1  in  FIG. 8  (step S 2  in  FIG. 8 ), and stores the calculated white balance correction values in the memory  24 . 
     Specifically, the controller  25  respectively calculates an average value RPA of R-component pixel values, an average value GPA of G-component pixel values, and an average value BPA of B-component pixel values, for the respective sampling pixels included in the region for white balance adjustment  102   a , for example, and then calculates the white balance correction values for setting the ratio of the calculated three average values RPA, GPA, and BPA as 1:1:1. 
     Then, the controller  25  extracts a region corresponding to the region for pixel shift correction  102   b  of the bottom surface portion  102  from the same image used for the extraction of the region for white balance adjustment  102   a  in the step S 1  in  FIG. 8  (step S 3  in  FIG. 8 ). 
     The controller  25  calculates the pixel shift correction values of the respective pixels included in the same image used for the extraction of the region for pixel shift correction  102   b  in the step S 3  in  FIG. 8  (step S 4  in  FIG. 8 ), and then writes the calculated pixel shift correction values of the respective pixels into the mapping table MPT1 or MPT2 in the memory  24 . 
     Now, description will be made on one example of calculation performed when calculating the pixel shift correction values in the step S 4  in  FIG. 8 . Hereinafter, for simplification, description will be made by taking the case where the pixel shift correction values in the vertical direction are calculated, as a main example. 
     First, the controller  25  divides the coordinate positions of the respective sampling pixels included in the mapping table MPT1 or MPT2 in the memory  24  into a group GR1 included in the center portion of the region for pixel shift correction  102   b  and a group GR2 included in a peripheral portion other than the center portion.  FIG. 9  schematically illustrates how to divide into the group GR1 and the group GR2 in the processing related to the calculation of pixel shift correction values. 
     Specifically, when the image size of the region for pixel shift correction  102   b  is 400×400 pixels, for example, the controller  25  divides the coordinate positions of the respective sampling pixels included in the mapping table MPT1 or MPT2 in the memory  24  into the group GR1 included in a range (region) of 150×150 pixels located at the center portion of the region for pixel shift correction  102   b  and the group GR2 included in the peripheral portion other than the center portion, as schematically shown in  FIG. 9 . Such a manner how to divide into the group GR1 and the group GR2 shows one example in the case where the distance between the distal end surface of the insertion portion  11  and the bottom surface portion  102  is a predetermined distance. Therefore, with the present embodiment, the ranges (regions) of the center portion and the peripheral portion of the region for pixel shift correction  102   b  are preferably set to be ranges (regions) having suitable sizes in accordance with the distance between the distal end surface of the insertion portion  11  and the bottom surface portion  102 . 
     Next, the controller  25  extracts the coordinate positions of the respective sampling pixels constituting the segments in the horizontal direction of the lattice pattern of the region for pixel shift correction  102   b  from the coordinate positions of the respective sampling pixels which belong to the group GR1 or GR2. Specifically, the controller  25  extracts the part drawn in the second color in the region for pixel shift correction  102   b , for example, as the coordinate positions of the respective sampling pixels constituting the segments in the horizontal direction of the lattice pattern of the pixel shift correction region  102   b.    
     Given the case where the coordinate positions of the respective sampling pixels constituting one segment in the horizontal direction of the lattice pattern of the region for pixel shift correction  102   b  are represented by (xi, yi) (in this regard, 0≦i≦N−1), and a spline curve in the horizontal direction, which is calculated based on the coordinate positions of the respective sampling pixels, is represented by f (xi), an evaluation value σ corresponding to the spline curve f (xi) can be expressed by the following equation (1). In the following equation (1), ωi represents a predetermined constant number, g represents a weighting factor which is a positive value, and f (M)  (xi) represents M-th derivative function of the spline curve f (xi). 
     
       
         
           
             
               
                 
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     The first item on the right side of the equation (1) is treated as a scale for measuring to what extent the spline curve f (xi) is separated from the coordinate positions (x0, y0), (x1, y1), . . . (x (N−1), y (N−1) of the respective sampling pixels constituting one segment in the horizontal direction of the lattice pattern of the region for pixel shift correction  102   b . Therefore, as the value of the first item on the right side of the equation (1) becomes smaller, for example, the separation between the coordinate positions (x0, y0), (x1, y1), . . . (x (N−1), y (N−1) of the respective sampling pixels constituting the one segment in the horizontal direction of the lattice pattern of the region for pixel shift correction  102   b  and the spline curve f (xi) becomes smaller. 
     In addition, the second item on the right side of the equation (1) is treated as a scale for expressing the magnitude of the fluctuation of the spline curve f (xi). Therefore, as the value except for the weighting factor g in the second item on the right side of the equation (1) becomes smaller, for example, the spline curve f (xi) becomes smoother. 
     That is, the pixel shift correction values in the vertical direction corresponding to the Y-coordinate values yi can be calculated by calculating the spline curve f (xi) for which the evaluation value σ on the left side of the equation (1) becomes minimum, and by further obtaining a difference between the calculated spline curve f (xi) in the horizontal direction and the Y-coordinate values yi of the sampling pixels (by performing calculation of f(xi)-yi). In addition, with the calculation using the above-described equation (1), for example, the pixel shift correction values in the horizontal direction corresponding to the X-coordinate values can be also calculated by calculating the spline curve in the vertical direction for which the evaluation value 6 on the left side of the equation (1) becomes minimum, and further obtaining a difference between the calculated spline curve in the vertical direction and the X-coordinate values of the sampling pixels. 
     When scanning is performed (the illumination fibers  12  are swung) in a spiral scanning pattern, the amount of shift of the coordinate positions of the sampling pixels which belong to the group GR1 as the region where the scanning density is the highest is considered to become relatively large in relation to the amount of shift of the coordinate positions of the sampling pixels which belong to the group GR2. 
     In response to the above-described matter, with the present embodiment, in order to address the occurrence of distortion in the case where the scanning is performed in the spiral scanning pattern, the value of the weighting factor g applied to the equation (1) when calculating the pixel shift correction values of the respective sampling pixels which belong to the group GR1 is set to be larger than the value of the weighting factor g applied to the equation (1) when calculating the pixel shift correction values of the respective sampling pixels which belong to the group GR2, for example, to thereby allow the pixel shift correction values based on the spline curves different from each other to be calculated in the two groups GR1 and GR2. 
     In other words, with the present embodiment, in order to address the occurrence of distortion in the case where the scanning is performed in the spiral scanning pattern, a first spline curve to be used for calculating the pixel shift correction values of the respective sampling pixels which belong to the group GR1 is calculated with the equation (1) in which the value of the weighting factor g is set so as to place emphasis on the smoothness of the spline curve itself, while a second spline curve to be used for calculating the pixel shift correction values of the respective sampling values which belong to the group GR2 is calculated with the equation (1) in which the value of the weighting factor g is set so as to place emphasis on the low degree of separation of the spline curve with respect to the coordinate positions of the sampling pixels, for example. 
     The present embodiment enables the spline curves preferable for calculating the pixel shift correction values to be calculated not only for addressing the distortion which occurs in the case where the scanning is performed in the spiral scanning pattern but also for addressing the distortion which occurs in the case where scanning is performed in another scanning pattern, by appropriately changing the setting of the value of the weighting factor g in the equation (1). 
     In addition, in the present embodiment, for example, the range (region) of the group GR1 may be set to partly overlap the range (region) of the group GR2, to enable a smooth connection of the first spline curve to be used for calculating the pixel shift correction values of the respective sampling pixels which belong to the group GR1 and the second spline curve to be used for calculating the pixel shift correction values of the respective sampling pixels which belong to the group GR2. 
     Furthermore, with the present embodiment, weighting depending on the distance between the pixels is performed on either the pixel shift correction values calculated in the respective pixels which belong to the group GR1 or the pixel shift correction values calculated in the respective pixels which belong to the group GR2, for example, to enable also the pixel shift correction values in the respective interpolation pixels and in the respective pixels included in the region for white balance adjustment  102   a  to be calculated. 
     That is, the above-described calculation is performed in the step S 4  in  FIG. 8 , and thereby the pixel shift correction values in the horizontal direction and the pixel shift correction values in the vertical direction are calculated for the respective pixels included in the same image as the one used for the extraction of the region for pixel shift correction  102   b  in the step S 3  in  FIG. 8 , and the calculated pixel shift correction values in the horizontal and vertical directions are written into the mapping table MPT1 or MPT2 in the memory  24 . 
     The controller  25  performs the processing in the step S 4  in  FIG. 8 , and then determines whether the pixel shift correction values for the two mapping tables MPT1 and MPT2 are calculated by confirming the information stored in the memory  24  (step S 5  in  FIG. 8 ). 
     When the controller  25  acquires the determination result that the pixel shift correction values have not been calculated for either the mapping table MPT1 or the mapping table MPT2, the controller  25  returns to the step S 3  in  FIG. 8  to perform the processing in the step S 3 . 
     In addition, when the controller  25  acquires the determination result that the pixel shift correction values are calculated for both of the mapping tables MPT1 and MPT2, the controller  25  generates corrected images for two frames which are respectively subjected to the white balance adjustment processing using the white balance correction values stored in the memory  24  and the pixel shift correction processing using the pixel shift correction values written into the mapping tables MPT1 and MPT2 stored in the memory  24  (step S 6  in  FIG. 8 ). 
     After that, the controller  25  determines whether the white balance adjustment processing and the pixel shift correction processing are normally performed on both of the corrected images for two frames which were generated in the step S 6  in  FIG. 8  (step S 7  in  FIG. 8 ). 
     When the controller  25  acquires the determination result that the white balance adjustment processing and the pixel shift correction processing have not been normally performed on either one of the images for two frames generated in the step S 6  in  FIG. 8 , the controller  25  respectively abandons the white balance correction values stored in the memory  24  and the pixel shift correction values written into the mapping tables MPT1 and MPT2 stored in the memory  24 , and then performs the processing from the step S 1  in  FIG. 8  again. 
     In addition, when the controller  25  acquires the determination result that the white balance adjustment processing and the pixel shift correction processing have been normally performed on both of the images for two frames generated in the step S 6  in  FIG. 8 , the controller  25  saves in the memory  24  the corrected images for two frames and the endoscope information read from the memory  16  of the scanning endoscope  2  connected to the main body apparatus  3  in association with each other (step S 8  in  FIG. 8 ), and then completes a series of processing for acquiring the white balance correction values and the pixel shift correction values. 
     Specifically, the controller  25  causes the corrected images for two frames generated in the step S 6  in  FIG. 8  and a GUI (Graphical User Interface) for urging the operator or the like to select whether or not the white balance adjustment processing and the pixel shift correction processing are normally performed to be displayed together on the monitor  4 , for example. When the controller  25  detects that a GUI button on which character strings indicating negative such as “NO” are written is depressed by the operator or the like based on the operation of a keyboard or a pointing device (neither not shown) by the operator or the like, for example, the controller  25  acquires the determination result that the white balance adjustment processing and the pixel shift correction processing have not been normally performed on either one of the corrected images for two frames generated in the step S 6  in  FIG. 8 . When the controller  25  detects that a GUI button on which character strings indicating affirmative such as “YES” is written is depressed based on the operation of the keyboard or a pointing device (neither not shown) by the operator or the like, for example, the controller  25  acquires the determination result that the white balance adjustment processing and the pixel shift correction processing are normally performed on both of the corrected images for two frames generated in the step S 6  in  FIG. 8 . 
     The controller  25  has a function as a determination section, and determines the necessity or unnecessity of the acquisition of the pixel shift correction values with reference to the endoscope information and the corrected images that are saved in association with each other in the memory  24 , and executes or omits the processing steps corresponding to the steps S 3  to S 8  in  FIG. 8  based on the determination result. 
     Specifically, when the controller  25  reads from the memory  16  the same endoscope information as that already saved in the memory  24  and detects that a difference value (a value corresponding to a distortion amount or a pixel shift amount) between the corrected images stored in association with the endoscope information and the images before correction which were generated based on the sampling pixels and the interpolation pixels before performing the processing in the step S 1  in  FIG. 8  is equal to or smaller than a predetermined threshold, for example, the controller  25  operates so as to determine that the acquisition of the pixel shift correction value is unnecessary and then omit the processing steps corresponding to the steps S 3  to S 8  in  FIG. 8  based on the determination result. 
     On the other hand, when the controller  25  reads from the memory  16  the same endoscope information as that already saved in the memory  24 , and detects that the difference value (the value corresponding to the distortion amount or the pixel shift amount) between the corrected images stored in association with the endoscope information and the images before correction which were generated based on the sampling pixels and the interpolation pixels before performing the processing in the step S 1  in  FIG. 8  is larger than a predetermined threshold, for example, the controller  25  operates so as to determine that the acquisition of the pixel shift correction values is necessary and then execute the processing steps corresponding to the steps S 3  to S 8  in  FIG. 8  based on the determination result. 
     As described above, the present embodiment enables the white balance correction values and the pixel shift correction values in the images can be collectively acquired, based on the images acquired by scanning the region for white balance adjustment  102   a  and the region for pixel shift correction  102   b  of the test chart device  101 . Therefore, the present embodiment enables the amount of operation required for observation using the scanning endoscope to be reduced. 
     In addition, as described above, with the present embodiment, the controller  25  is configured to determine the necessity or unnecessity of the acquisition of the pixel shift correction values in the scanning endoscope  2  which has been connected to the main body apparatus  3  in the past. Therefore, the present embodiment enables a part of operations performed before the observation using the scanning endoscope to be omitted, i.e., there is no need for the operator to visually check the images to determine the necessity or unnecessity of the acquisition of the pixel shift correction values, every time when the scanning endoscope  2  is connected to the main body apparatus  3 . As a result, the amount of work required for observation using the scanning endoscope can be reduced. 
     In the present embodiment, when the pixel values of respective color components are indicated with the values from 0 to 255 (eight bits), a series of processing steps in  FIG. 8  may be performed by previously eliminating the pixels whose pixel values of the R component, G component, and B component are all 255, for example. 
     The present invention is not limited to the above-described embodiment, and it is needless to say that various changes and modifications are possible without departing from the gist of the invention.