Patent Publication Number: US-9848124-B2

Title: Endoscope system and endoscope video processor

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of PCT/JP2015/085510 filed on Dec. 18, 2015 and claims benefit of Japanese Application No. 2014-258920 filed in Japan on Dec. 22, 2014, the entire contents of which are incorporated herein by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an endoscope system and an endoscope video processor, and more particularly to an endoscope system capable of observing a forward field of view and a lateral field of view independently and simultaneously, and an endoscope video processor. 
     2. Description of the Related Art 
     Endoscope systems provided with an endoscope for picking up an image of an object inside a subject, an image processing apparatus for generating an observed image of the object picked up by the endoscope, and the like are widely known in a medical field, an industrial field and the like. 
     Further, some endoscope systems are capable of observing a subject with a wide field of view in order to prevent a lesion portion from being overlooked. For example, Japanese Patent Application Laid-Open Publication No. 2013-66648 discloses an endoscope capable of simultaneously acquiring a forward-field-of-view image and a lateral-field-of-view image and displaying the forward-field-of-view image and the lateral-field-of-view image on a display portion. 
     SUMMARY OF THE INVENTION 
     An endoscope system of an aspect of the present invention includes: an insertion portion configured to be inserted into an inside of an object; a first object image acquiring portion provided on the insertion portion and configured to acquire a first object image from a first area of the object; a second object image acquiring portion provided on the insertion portion and configured to acquire a second object image from a second area of the object different from the first area; an image pickup portion configured to pick up the first object image and the second object image; an object image position detecting portion configured to detect a positional relationship between a first image forming area where the first object image is formed and a second image forming area where the second object image is formed, on the image pickup portion and generate positional relationship detection information; and an image signal generating portion configured to generate an image signal in which the first object image and the second object image are arranged with a first reference position provided in the first image forming area and a second reference position provided in the second image forming area caused to correspond to each other based on the positional relationship detection information. 
     An endoscope video processor of the present invention is an endoscope video processor into which a first object image acquired by an image pickup portion of an endoscope inserted inside an object and a second object image acquired from a direction different from a direction for the first object image are inputted, the endoscope video processor including: an object image position detecting portion configured to detect a positional relationship between a first image forming area where the first object image is formed on the image pickup portion and a second image forming area where the second object image is formed on the image pickup portion and generate positional relationship detection information; and an image signal generating portion configured to generate an image signal in which the first object image and the second object image are arranged with a first reference position provided in the first image forming area and a second reference position provided in the second image forming area caused to correspond to each other based on the positional relationship detection information. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a configuration of an endoscope system according to a first embodiment of the present invention; 
         FIG. 2  is a perspective view showing a configuration of a distal end portion of an insertion portion of an endoscope according to the first embodiment of the present invention; 
         FIG. 3  is a front view showing the configuration of the distal end portion of the insertion portion of the endoscope according to the first embodiment of the present invention; 
         FIG. 4  is a sectional view of main portions showing the configuration of the distal end portion of the insertion portion in the endoscope system of the first embodiment of the present invention; 
         FIG. 5  is a diagram showing an example of an observed image displayed on a monitor by image processing by a video processor of the endoscope system according to the first embodiment of the present invention; 
         FIG. 6  is a block diagram showing a configuration of a video processor  32  according to the first embodiment of the present invention; 
         FIG. 7  is a block diagram showing configurations of a positional displacement correcting portion  65  and a boundary correcting portion  66  according to the first embodiment of the present invention; 
         FIG. 8  is a diagram for illustrating a positional displacement between a center CF of a forward-field-of-view image portion FVa projected on an image pickup surface  40   a  of an image pickup device  40  and a center CS of a lateral-field-of-view image portion SVa in a center coordinates estimating portion  71  according to the first embodiment of the present invention; 
         FIG. 9  is a diagram for illustrating a process by a cutting out portion  73 , an enlarging portion  74  and a combining portion  67  according to the first embodiment of the present invention; 
         FIG. 10  is a simplified schematic perspective view of a distal end portion  6  of an endoscope  2 A according to a second embodiment of the present invention; 
         FIG. 11  is a schematic configuration diagram showing an internal configuration of the distal end portion  6  according to the second embodiment of the present invention; 
         FIG. 12  is a block diagram showing a configuration of a video processor  32 A according to the second embodiment of the present invention; 
         FIG. 13  is a diagram showing an example of an observed image displayed on a monitor  35  by image processing by the video processor  32 A of an endoscope system  1 A according to the second embodiment of the present invention; 
         FIG. 14  is a perspective view showing a configuration of a cap  91  according to the second embodiment of the present invention; 
         FIG. 15  is a diagram for illustrating displacements of object images formed on image pickup surfaces of respective image pickup devices  40 A,  40 B and  40 C according to the second embodiment of the present invention; 
         FIG. 16  is a diagram for illustrating an example in which positional displacement correction according to the second embodiment of the present invention has been performed; and 
         FIG. 17  is a perspective view of a distal end portion  6   a  of an insertion portion  4  to which a unit for lateral observation is fitted, according to a modification of the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Embodiments of the present invention will be described below with reference to drawings. 
     First Embodiment 
     (System Configuration) 
     First, description will be made on a configuration of an endoscope system of a first embodiment with use of  FIGS. 1 to 4 .  FIG. 1  is a diagram showing a configuration of an endoscope system according to the first embodiment.  FIG. 2  is a perspective view showing a configuration of a distal end portion of an insertion portion of an endoscope.  FIG. 3  is a front view showing the configuration of the distal end portion of the insertion portion of the endoscope.  FIG. 4  is a sectional view of main portions showing the configuration of the distal end portion of the insertion portion in the endoscope system of the first embodiment.  FIG. 5  is a diagram showing an example of an observed image displayed on a monitor by image processing by a video processor of the endoscope system. 
     As shown in  FIG. 1 , an endoscope system  1  has an endoscope  2  configured to pick up an image of an observation target substance (an object) and output an image pickup signal, a light source apparatus  31  configured to supply illuminating light for illuminating the observation target substance, a video processor  32  which is an image processing apparatus configured to generate and output a video signal corresponding to the image pickup signal, and a monitor  35  configured to display an observed image which is an endoscopic image corresponding to the video signal. 
     The endoscope  2  is configured having an operation portion  3  configured to be grasped by a surgeon to perform an operation, an elongated insertion portion  4  formed on a distal end side of the operation portion  3  and configured to be inserted into a body cavity or the like, which is an object, and a universal cord  5  one end portion of which is provided so as to extend from a side portion of the operation portion  3 . 
     The endoscope  2  of the present embodiment is a wide-angle endoscope making it possible to observe a field of view of 180 degrees or more by causing a plurality of field-of-view images to be displayed. It is realized to prevent a lesion at such a place that it is difficult to see the lesion only by front observation, such as a back of folds and a boundary of organs, from being overlooked in a body cavity, especially in a large intestine. At time of inserting the insertion portion  4  of the endoscope  2  into a large intestine, actions such as a twist, a reciprocating motion and a temporary fixation by hooking an intestinal wall occur on the insertion portion  4 , similarly to an ordinary large intestine endoscope. 
     The insertion portion  4  to be inserted into an inside of an object is configured having a rigid distal end portion  6  provided on a most distal end side, a bendable bending portion  7  provided at a rear end of the distal end portion  6 , and a long flexible tube portion  8  having flexibility provided on a rear end of the bending portion  7 . Further, the bending portion  7  performs a bending action corresponding to an operation of a bending operation lever  9  provided on the operation portion  3 . 
     On the other hand, as shown in  FIG. 2 , a cylindrical portion  10  in a cylindrical shape provided projecting from a position eccentrically displaced upward from a center of a distal end face of the distal end portion  6  is formed on the distal end portion  6  of the insertion portion  4 . 
     On a distal end portion of the cylindrical portion  10 , an objective optical system not shown is provided which is for observation of both of a forward field of view and a lateral field of view. Further, the distal end portion of the cylindrical portion  10  is configured having a forward observation window  12  arranged at a position corresponding to a forward direction of the objective optical system not shown, and a lateral observation window  13  arranged at a position corresponding to a lateral-viewing direction of the objective optical system not shown. Furthermore, lateral illuminating windows  14  configured to emit light for illuminating a lateral direction are formed in a vicinity of a proximal end of the cylindrical portion  10 . The lateral observation window  13  is arranged on a more proximal end side of the insertion portion  4  than the forward observation window  12 . 
     The lateral observation window  13  is provided with a lateral-viewing mirror lens  15  for making it possible to acquire a lateral-field-of-view image by capturing return light, that is, reflected light from an observation target substance which is caused to be incident from around the cylindrical portion  10  in a cylindrical shape within a lateral field of view. 
     Note that, at an image forming position of the objective optical system not shown, an image pickup surface of an image pickup device  40  is arranged so that an image of an observation target substance within a field of view of the forward observation window  12  is formed at a central part as a circular-shaped forward-field-of-view image, and an image of the observation target substance within a field of view of the lateral observation window  13  is formed on an outer circumferential portion of the forward-field-of-view image as a ring-shaped lateral-field-of-view image. 
     That is, the forward observation window  12  is provided on the insertion portion  4  and constitutes a first object image acquiring portion configured to acquire a first object image from a first area including a forward direction, which is a first direction, and the lateral observation window  13  is provided on the insertion portion  4  and constitutes a second object image acquiring portion configured to acquire a second object image from a second area including a lateral direction, which is a second direction different from the forward direction. In other words, the forward observation window  12  is a forward image acquiring portion configured to acquire an object image in an area including the forward direction of the insertion portion, and the lateral observation window  13  is a lateral image acquiring portion configured to acquire an object image in an area including the lateral direction of the insertion portion. 
     The forward observation window  12  is arranged on the distal end portion  6  in a longitudinal direction of the insertion portion  4  so as to acquire an object image from the forward direction, which is a direction in which the insertion portion  4  is inserted, and the lateral observation window  13  is arranged along an outer diameter direction of the insertion portion  4  so as to acquire an object image from the lateral direction. In other words, the first object image is an object image in the first direction including the forward direction of the insertion portion substantially parallel to the longitudinal direction of the insertion portion  4 , and the second object image is an object image in the second direction including the lateral direction of the insertion portion crossing the longitudinal direction of the insertion portion  4 , for example, at a right angle. 
     Then, the image pickup device  40 , which is an image pickup portion, photoelectrically converts the forward-field-of-view image and the lateral-field-of-view image on one image pickup surface, and an image signal of the forward-field-of-view image and an image signal of the lateral-field-of-view image are generated by being cut out from the images obtained by the image pickup device  40 . That is, the image pickup device  40  constitutes an image pickup portion configured to pick up the first object image and the second object image, and the image pickup device  40  is electrically connected to the video processor  32 . 
     On the distal end face of the distal end portion  6 , a forward illuminating window  16  arranged at a position adjoining the cylindrical portion  10  and configured to emit illuminating light within a range of the forward field of view of the forward observation window  12 , and a distal end opening  17  communicating to a treatment instrument channel not shown, which is arranged in the insertion portion  4  and formed by a tube or the like, and capable of causing a distal end portion of a treatment instrument inserted in the treatment instrument channel to project. 
     Further, the distal end portion  6  of the insertion portion  4  has a support portion  18  provided so as to project from the distal end face of the distal end portion  6 , and the support portion  18  is positioned adjoining a lower part side of the cylindrical portion  10 . 
     The support portion  18  is configured being capable of supporting or holding respective projecting members arranged so as to be caused to project from the distal end face of the distal end portion  6 . More specifically, the support portion  18  is configured so as to be capable of supporting or holding each of a forward observation window nozzle portion  19  configured to eject gas or liquid for cleaning the forward observation window  12 , and lateral observation window nozzle portions  22  configured to eject gas or liquid for cleaning another forward illuminating window  21  configured to emit light for illuminating the forward direction and the lateral observation window  13 , as the respective projecting members described above. 
     On the other hand, the support portion  18  is formed having a blocking portion  18   a , which is an optical blocking member for preventing such a lateral-field-of-view image that includes any of the respective projecting members described above, which are substances different from an original observation target substance, from being acquired by the respective projecting members appearing in the lateral field of view. That is, by providing the blocking portion  18   a  on the support portion  18 , it is possible to obtain such a lateral-viewing field-of-view image that includes none of the forward observation window nozzle portion  19 , the forward illuminating window  21  and the lateral observation window nozzle portions  22 . 
     As shown in  FIGS. 2 and 3 , the lateral observation window nozzle portions  22  are provided at two positions of the support portion  18  and arranged so that distal ends project from a side face of the support portion  18 . 
     As shown in  FIG. 1 , the operation portion  3  is provided with a air/liquid feeding operation button  24   a  capable of giving an operation instruction to cause gas or liquid for cleaning the forward observation window  12  to be ejected from the forward observation window nozzle portion  19 , and a air/liquid feeding operation button  24   b  capable of giving an operation instruction to cause gas or liquid for cleaning the lateral observation window  13  to be ejected from the lateral observation window nozzle portions  22 . It is possible to switch between air feeding and liquid feeding by pressing down the air/liquid feeding operation buttons  24   a  and  24   b . Further, though the plurality of air/liquid feeding operation buttons are provided to correspond to the respective nozzle portions in the present embodiment, it is also possible, for example, to cause gas or liquid to be ejected from both of the forward observation window nozzle portion  19  and the lateral observation window nozzle portions  22  by an operation of one air/liquid feeding operation button. 
     A plurality of scope switches  25  are provided on a top portion of the operation portion  3  and have a configuration in which functions for the respective switches can be allocated so as to cause described various signals corresponding to on or off, which are usable in the endoscope  2 , to be outputted. More specifically, start and stop of forward water feeding, execution and release of freeze for photographing a still image, and a function of causing a signal corresponding to a notification of a use state of a treatment instrument and the like to be outputted can be allocated as functions of the respective switches. 
     Note that, in the present embodiment, a function of at least one of the air/liquid feeding operation buttons  24   a  and  24   b  may be allocated to any one of the scope switches  25 . 
     Further, on the operation portion  3 , a suction operation button  26  capable of giving an instruction to suck and collect mucus and the like in a body cavity from the distal end opening  17  to a suction unit or the like not shown is arranged. 
     The mucus and the like in the body cavity sucked in response to an action of the suction unit or the like not shown is collected into a suction bottle or the like of the suction unit not shown via the distal end opening  17 , the treatment instrument channel not shown in the insertion portion  4 , and a treatment instrument insertion port  27  provided near a front end of the operation portion  3 . 
     The treatment instrument insertion port  27  communicates to the treatment instrument channel not shown in the insertion portion  4  and is formed as an opening through which a treatment instrument not shown can be inserted. That is, a surgeon can perform treatment using a treatment instrument by inserting the treatment instrument from the treatment instrument insertion port  27  and causing a distal end side of the treatment instrument to project from the distal end opening  17 . 
     On the other hand, as shown in  FIG. 1 , the other end portion of the universal cord  5  is provided with a connector  29  connectable to the light source apparatus  31 . 
     A distal end portion of the connector  29  is provided with a pipe sleeve (not shown) to be a liquid conduit connection end portion and a light guide pipe sleeve (not shown) to be an illuminating light supply end portion. Further, an electrical contact portion (not shown) to which one end portion of a connection cable  33  can be connected is provided on a side face of the connector  29 . Furthermore, the other end portion of the connection cable  33  is provided with a connector for electrically connecting the endoscope  2  and the video processor  32 . 
     The universal cord  5  includes a plurality of signal lines for transmitting various electrical signals and a light guide for transmitting illuminating light supplied from the light source apparatus  31  in a bundled state. 
     The light guide included in the insertion portion  4  to the universal cord  5  has such a configuration that a light-emission-side end portion is branched in at least two directions near the insertion portion  4 , and a light emission end face on one side is arranged in the forward illuminating windows  16  and  21 , while a light emission end face on the other side is arranged in the lateral illuminating windows  14 . Further, the light guide has such a configuration that an end portion on a light incidence side is arranged in the light guide pipe sleeve of the connector  29 . 
     The video processor  32 , which is an image processing apparatus and an image signal generation apparatus, outputs a drive signal for driving the image pickup device  40  provided on the distal end portion  6  of the endoscope  2 . Then, the video processor  32  performs signal processing (cutting out a predetermined area) for an image pickup signal outputted from the image pickup device  40  based on a use state of the endoscope  2 , and, thereby, generate a video signal and output the video signal to the monitor  35 . 
     Peripheral devices such as the light source apparatus  31 , the video processor  32  and the monitor  35  are arranged on a stand  36  together with a keyboard  34  for performing input of patient information and the like. 
     The light source apparatus  31  includes a lamp. Light emitted from the lamp is guided to a connector portion to which the connector  29  of the universal cord  5  is connected, via the light guide. The light source apparatus  31  supplies illuminating light to the light guide in the universal cord  5 . 
       FIG. 4  is a sectional view of main portions showing a configuration of the distal end portion  6  of the insertion portion  4  in the endoscope system of the first embodiment, which shows a configuration of an objective optical system  11  covering the forward direction and the lateral direction, and peripheral portions of the lateral illuminating windows  14 . 
     The objective optical system  11  which forms an image on the image pickup device  40  is formed by arranging a forward lens  41 , a mirror lens  15  and a rear lens group  43 , each lens being in a rotationally symmetrical shape, on an optical axis corresponding to an image pickup center O along a central axis of the cylindrical portion  10  projecting from the distal end portion  6 . Note that cover glass  42  is provided on a front face of the image pickup device  40 . The forward lens  41 , the mirror lens  15  and the rear lens group  43  are fixed to a lens frame in the cylindrical portion  10 . 
     The forward lens  41  constituting the objective optical system  11  and provided in the circular-shaped forward observation window  12  forms a wide-angle forward field of view, with its distal end side along an insertion direction of the insertion portion  4  as an observation field of view. 
     The mirror lens  15  as a catoptric system, which is arranged immediately after the forward lens  41 , is configured as shown in  FIG. 4  by what is obtained by bonding two lenses together which reflect light caused to be incident from a side face direction twice by a bonded surface and a front face to guide the light to the rear lens group  43  side. 
     Note that a lens part of the mirror lens  15  facing the forward lens  41  also has a function of refracting light from the forward lens  41  and guiding the light to the rear lens group  43  side. 
     By the mirror lens  15  provided in the lateral observation window  13 , the lateral observation window  13  forms a substantially ring-shaped observation field of view covering an entire circumference in a circumferential direction of the insertion portion while having a predetermined view angle, with an optical axis in a lateral direction relative to a long axis direction of the insertion portion as a substantial center. 
     Note that  FIG. 4  shows schematic routes of a light beam incident on the forward lens  41  forming the forward observation window  12  from an object side within its field of view and a light beam incident on the mirror lens  15  forming the lateral observation window  13  from the object side within its field of view. 
     On the image pickup surface of the image pickup device  40 , an image of an object within the forward field of view provided facing the insertion direction by the forward lens  41  of the forward observation window  12  is formed in a circular shape on a center side, and the image is acquired as a forward-field-of-view image. Further, on the image pickup surface, an image of the object within the lateral field of view is formed in a ring shape by the mirror lens  15  facing the lateral observation window  13  on an outer circumference side of the forward-field-of-view image, and the image is acquired as a lateral-field-of-view image. 
     In the present embodiment, however, the blocking portion  18   a  configured to mechanically block light from the object side which is incident into the ring-shaped lateral field of view is formed by the support portion  18 . Further, in the present embodiment, a configuration is adopted in which lateral illuminating light emitted in the side-face direction from the lateral illuminating windows  14  side is not emitted to the support portion  18  side. 
     Note that, though a lateral-field-of-view image is acquired with use of the catoptric system twice in the present embodiment as a method for forming a forward-field-of-view image and a lateral-field-of-view image on one image pickup device, the lateral-field-of-view image may be acquired with the use of the catoptric system once. In the case of using the catoptric system once, an image direction of the lateral-field-of-view image may be adjusted by image processing or the like as necessary. 
     The lateral illuminating windows  14  are provided at a plurality of positions on an outer circumferential face near the proximal end adjoining the lateral observation window  13  on the cylindrical portion  10 . In the present embodiment, the lateral illuminating windows  14  are provided at two positions on both of left and right sides in a circumferential direction, and lateral illuminating light is emitted to a whole area in the circumferential direction except the lower part side where the support portion  18  is provided. 
     As shown in  FIG. 4 , a distal end side of the light guide  44  as a light emitting member arranged along a longitudinal direction of the distal end portion  6  is extended to a vicinity of a proximal end of a cylindrical member  10   a  constituting the cylindrical portion  10  projecting from the distal end face of the distal end portion  6 . 
     In the vicinity of the proximal end of the cylindrical portion  10  (on an outer circumference side of the rear lens group  43 ), a distal end face of the light guide  44  is arranged near its side face, and the distal end face of the light guide  44  becomes an emission end face for emitting guided light, and the light is emitted in a distal end direction. Though the emission end face is in a circular shape in the present embodiment, the emission end face is not limited to the circular shape, and different shapes, including an oval and a polygon, are also possible. 
     At a position which the emission end face faces, a concave portion forming a light guiding groove  45  as a groove portion configured to guide light is provided, the concave portion extending long in band shape along an outer circumference of the cylindrical-shaped side face of the cylindrical portion  10  with the position as a center. A reflecting member  46  as an illumination reflecting portion formed to face the emission end face is arranged in the concave portion, and the light guiding groove  45  provided with a reflecting portion  46   a  configured to reflect light is formed on an internal surface of the reflecting member  46 . 
     As for the reflecting portion  46   a  on the internal surface of the light guiding groove  45  formed by the reflecting member  46  shows a concave face in a substantially semispherical shape on a longitudinal section shown in  FIG. 4 . Further, the semispherical-shaped concave surface of the reflecting portion  46   a  is formed longer than the emission end face of the light guide  44  along the circumferential direction of the cylindrical portion  10 . 
     The reflecting portion  46   a  reflects light emitted toward the distal end side of the distal end portion  6  from the emission end face by the reflecting portion  46   a  to change a travel direction of the light to the side face direction, guides the light to a wide-range side face direction along the circumferential direction and emits the light from the lateral illuminating windows  14  to illuminate an observation field of view side (an observation target side) of the lateral observation window  13 . Therefore, the light emitted to the side face direction from the light guiding groove  45  becomes lateral illuminating light. 
     Note that the reflecting portion  46   a  can be formed by providing a thin film of metal having a high reflectivity, such as aluminum, chromium, nickel chromium, silver and gold, on the internal surface of the reflecting member  46 . 
     Thus, in the present embodiment, the reflecting member  46  is arranged in the concave portion of the light guiding groove  45  so that the light guiding groove  45  provided with the reflecting portion  46   a  is formed long along outer circumference of the side face of the cylindrical portion  10 . Further, the emission end face of the light guide  44  as the light emitting member is arranged so as to be positioned near a central position in the circumferential direction in the reflecting member  46  or the light guiding groove  45 . 
     Light emitted from the emission end face of the light guide  44  is reflected by the reflecting portion  46   a  arranged so as to form a reflecting surface around the emission end face, and illuminating light is emitted in a wide range from the lateral illuminating windows  14  provided with the light guiding groove  45  in the lateral direction. 
       FIG. 5  shows an example of an endoscopic image displayed on the monitor  35 . An observed image  50 , which is an endoscopic image displayed on a display screen  35   a  of the monitor  35 , is a substantially rectangular image having two portions  52  and  53 . The portion  52  in a circular shape at a central part is a portion to display a forward-field-of-view image, and the portion  53  in a C shape around the portion  52  at the central part is a portion to display a lateral-field-of-view image. 
     Note that the images displayed in the portions  52  and  53  of the endoscopic image displayed on the monitor  35  are not necessarily same as an image of an object within the forward field of view and an image of the object within the lateral field of view, respectively. 
     That is, the forward-field-of-view image is displayed on the display screen  35   a  of the monitor  35  so as to be in a substantially circular shape, and the lateral-field-of-view image is displayed on the display screen  35   a  so as to be in a substantially ring shape surrounding at least a part of a circumference of the forward-field-of-view image. Therefore, a wide-angle endoscopic image is displayed on the monitor  35 . 
     The endoscopic image shown in  FIG. 5  is generated from an acquired image acquired by the image pickup device  40  ( FIG. 2 ). The observed image  50  is generated by photoelectrically converting an object image projected on the image pickup surface of the image pickup device  40  by the objective optical system provided in the distal end portion  6 , and combining a forward-field-of-view image portion at a center corresponding to the portion  52  and a lateral-field-of-view image portion corresponding to the portion  53  excluding a blacked mask area  54 . 
     (Configuration of Video Processor) 
       FIG. 6  is a block diagram showing a configuration of the video processor  32 . In  FIG. 6 , only components related to functions of the present embodiment described below are shown, and components related to other functions such as image recording are omitted. 
     The video processor  32  has a control portion  60 , an analog/digital converting portion (hereinafter referred to as an A/D conversion portion)  61 , a preprocessing portion  62 , a light-adjusting portion  63 , an enlarging/reducing portion  64 , a positional displacement correcting portion  65 , a boundary correcting portion  66 , a combining portion  67 , an image outputting portion  68  and a register  69 . The video processor  32  has a function of generating an image-processed image as described later. 
     Further, the endoscope  2  has a nonvolatile memory  70  such as a flash memory. Displacement amount data to be described later is written and stored into the memory  70  by the video processor  32  and can be read out by the video processor  32 . 
     The control portion  60  includes a central processing unit (CPU), a ROM, a RAM and the like. The control portion  60  executes a predetermined software program in response to an instruction such as a command input by the user from an operation panel not shown, and generates or reads out various kinds of control signals or data signals to control each necessary circuit and each necessary portion in the video processor  32 . 
     The A/D conversion portion  61  includes an A/D conversion circuit. The A/D conversion portion  61  is a circuit configured to convert an image pickup signal from the image pickup device  40  of the endoscope  2  from an analog signal to a digital signal. 
     The preprocessing portion  62  is a circuit configured to perform processing such as color filter conversion for an image pickup signal from the image pickup device  40  of the endoscope  2  to output a video signal. 
     The light-adjusting portion  63  is a circuit configured to judge brightness of an image based on the video signal and output a light adjustment control signal to the light source apparatus  31  based on a light adjustment state of the light source apparatus  31 . 
     The enlarging/reducing portion  64  enlarges or reduces an image of the video signal outputted from the preprocessing portion  62  in accordance with the size and format of the monitor  35 , and outputs a video signal of the enlarged or reduced image to the positional displacement correcting portion  65 . 
     The positional displacement correcting portion  65  executes a process for estimating two center coordinates of a forward-field-of-view image FV and a lateral-field-of-view image SV and calculating an amount of displacement between the two estimated center coordinates. The positional displacement correcting portion  65  stores the calculated amount of displacement into the memory  70  of the endoscope  2  as well as into the register  69 . 
     The positional displacement correcting portion  65  outputs a video signal which includes the inputted forward-field-of-view image FV and lateral-field-of-view image SV to the boundary correcting portion  66 . 
     The boundary correcting portion  66  cuts out the forward-field-of-view image FV and the lateral-field-of-view image SV from the inputted video signal using the displacement amount data stored in the register  69  and executes a predetermined enlargement process. 
       FIG. 7  is a block diagram showing configurations of the positional displacement correcting portion  65  and the boundary correcting portion  66 . 
     The positional displacement correcting portion  65  includes a center coordinates estimating portion  71  and a displacement amount calculating portion  72 . 
     The center coordinates estimating portion  71  is a circuit configured to calculate and estimate an amount of displacement between positions of a center CF of a forward-field-of-view image portion FVa and a center CS of a lateral-field-of-view image portion SVa on the image pickup surface  40   a  of the image pickup device  40 . 
     Since the forward-field-of-view image portion FVa and the lateral-field-of-view image portion SVa formed on the image pickup surface  40   a  by the optical system shown in  FIG. 4  are in a circular shape and a ring shape, respectively, the center coordinates estimating portion  71  can calculate the center CF of the circular-shaped forward-field-of-view image portion FVa and the center CS of the ring-shaped lateral-field-of-view image portion SVa. 
     The control portion  60  reads out data from the memory  70  of the endoscope  2  to judge whether the displacement amount data exists or not. If the displacement amount data is not stored in the memory  70 , the control portion  60  controls the positional displacement correcting portion  65  to cause the center coordinates estimating portion  71  and the displacement amount calculating portion  72  to operate. 
     As shown in  FIG. 7 , the boundary correcting portion  66  includes a cutting out portion  73  and an enlarging portion  74 . 
     The cutting out portion  73  is a circuit configured to cut out the forward-field-of-view image FV of the forward-field-of-view image portion FVa and the lateral-field-of-view image SV of the lateral-field-of-view image portion SVa from an inputted video signal based on the displacement amount data read out from the register  69  and output the forward-field-of-view image FV and the lateral-field-of-view image SV to the enlarging portion  74 . 
     The enlarging portion  74  performs an enlargement process for the cut-out forward-field-of-view image FV at a predetermined magnification and outputs the forward-field-of-view image FV to the combining portion  67 . 
     Returning to  FIG. 6 , the combining portion  67  combines the forward-field-of-view image FV and the lateral-field-of-view image SV so that the respective centers CF and CV of the inputted forward-field-of-view image FV and lateral-field-of-view image SV correspond to a center C of the image pickup surface  40   a  and outputs an image obtained by the combination to the image outputting portion  68 . 
     Note that the combining portion  67  also executes mask processing. 
     The image outputting portion  68  is a circuit as an image generating portion configured to generate an image signal which includes the forward-field-of-view image FV and the lateral-field-of-view image SV from the combining portion  67  by image processing, convert the image signal to a display signal and output the display signal to the monitor  35 . That is, the image outputting portion  68  inputs an image signal from the combining portion  67 , and the image outputting portion  68  generates a display signal for displaying the image signal based on the forward-field-of-view image FV and the lateral-field-of-view image SV on the monitor  35  which is a display portion. 
     (Operation) 
     Next, description will be made on an example of a procedure about a method for a process for correcting a positional displacement between a forward-field-of-view image and a lateral-field-of-view image in the video processor  32 . 
     First, the positional displacement between a forward-field-of-view image and a lateral-field-of-view image will be described. 
       FIG. 8  is a diagram for illustrating a positional displacement between a center CF of a forward-field-of-view image portion FVa projected on the image pickup surface  40   a  of the image pickup device  40  and a center CS of a lateral-field-of-view image portion SVa in the center coordinates estimating portion  71 . 
     On the image pickup surface  40   a  of the image pickup device  40 , a forward-field-of-view image portion FVa corresponding to a circular-shaped forward-field-of-view image FV by a forward-field-of-view optical system which includes the forward lens  41  of the forward observation window  12  and a lateral-field-of-view image portion SVa corresponding to a ring-shaped lateral-field-of-view image SV by a lateral-field-of-view optical system which includes the mirror lens  15  facing the lateral observation window  13  are formed. 
     As described above, due to variation and the like in processing accuracy of or at time of assembly of a frame for fixing each lens of the objective optical system or the image pickup device  40 , the center CF of the forward-field-of-view image portion FVa (shown by a dotted line) in a circular shape and the center CS of the lateral-field-of-view image portion SVa (shown by a one-dot chain line) in a ring shape may be relatively displaced as shown in  FIG. 8 . 
     Furthermore, the center CF of the forward-field-of-view image portion FVa and the center CS of the lateral-field-of-view image portion SVa may be displaced relative to the center C of the image pickup surface  40   a  of the image pickup device  40 . In  FIG. 8 , the center CF of the forward-field-of-view image portion FVa and the center CS of the lateral-field-of-view image portion SVa are also displaced relative to the center C of the image pickup surface  40   a.    
     Therefore, the positional displacement correcting portion  65  of the video processor  32  calculates an amount of relative displacement between the center CF of the forward-field-of-view image portion FVa and the center CS of the lateral-field-of-view image portion SVa or an amount of displacement of each of the center CF of the forward-field-of-view image portion FVa and the center CS of the lateral-field-of-view image portion SVa relative to the center C of the image pickup surface  40   a . Here, in the positional displacement correcting portion  65 , the amount of displacement of each of the center CF of the forward-field-of-view image portion FVa and the center CS of the lateral-field-of-view image portion SVa relative to the center C of the image pickup surface  40   a  are calculated. 
     For example, at time of manufacturing the endoscope  2 , a forward-field-of-view object image and a lateral-field-of-view object image are caused to be projected onto the image pickup surface  40   a  by picking up an appropriate object image by the distal end portion  6  of the insertion portion  4 , and the positional displacement correcting portion  65  is caused to operate. A video signal of an image which includes both of the forward-field-of-view image portion FVa and the lateral-field-of-view image portion SVa is inputted to the center coordinates estimating portion  71 . 
     Note that the center coordinates estimating portion  71  may be adapted to operate in response to a user instruction or may be adapted to automatically operate when it is judged that displacement amount data is not stored in the memory  70 . 
     The center coordinates estimating portion  71  extracts the forward-field-of-view image portion FVa and the lateral-field-of-view image portion SVa by image processing, based on luminance values of pixels of the inputted video signal and determines the center of each of the extracted portions. 
     For example, the center coordinates estimating portion  71  can extract a pixel area on the image pickup surface  40   a  corresponding to the circular-shaped forward-field-of-view image portion FVa and a pixel area on the image pickup surface  40   a  corresponding to the ring-shaped lateral-field-of-view image portion SVa based on difference among the luminance values of the respective pixels. 
     In  FIG. 8 , coordinates of the center CF of the forward-field-of-view image portion FVa on the image pickup surface  40   a  can be determined by assuming appropriate two straight lines L 1   a  and L 1   b  (shown by two-dot chain lines) passing through the circular-shaped forward-field-of-view image portion FVa and calculating an intersection point of perpendicular bisectors L 1   av  and L 1   bv  (shown by two-dot chain lines) for line segments of the straight lines L 1   a  and L 1   b  inside the circle, respectively. 
     Similarly, coordinates of the center CS of the lateral-field-of-view image portion SVa on the image pickup surface  40   a  can be obtained by assuming appropriate two straight lines L 2   a  and L 2   b  (shown by two-dot chain lines) passing through the ring-shaped lateral-field-of-view image portion SVa and calculating an intersection point of perpendicular bisectors L 2   av  and L 2   bv  for line segments of the straight lines L 2   a  and L 2   b  inside an outside circle of the lateral-field-of-view image portion SVa, respectively. 
     Coordinates of the center C of the image pickup surface  40   a  is indicated by (x0, y0); the obtained coordinates of the center CF of the forward-field-of-view image portion FVa is indicated by (xf1, yf1); and the obtained coordinates of the center CS of the lateral-field-of-view image portion SVa is indicated by (xs1, ys1). 
     The displacement amount calculating portion  72  calculates the amounts of displacement from the center CF of the forward-field-of-view image portion FVa and the center CS of the lateral-field-of-view image portion SVa determined by the center coordinates estimating portion  71 . 
     An amount of displacement dfx of the center CF in an x-axis direction relative to the center C of the image pickup surface  40   a  is indicated by an equation (1).
 
 Dfx =( xf 1− x 0)  (1)
 
     Further, an amount of displacement dfy of the center CF in a y-axis direction relative to the center C of the image pickup surface  40   a  is indicated by an equation (2).
 
 Dfy =( yf 1− y 0)  (2)
 
     Similarly, an amount of displacement dsx of the center CS in the x-axis direction relative to the center C of the image pickup surface  40   a  is indicated by an equation (3).
 
 Dsx =( xs 1− x 0)  (3)
 
     Further, an amount of displacement dsy of the center CS in the y-axis direction relative to the center C of the image pickup surface  40   a  is indicated by an equation (4).
 
 Dsy =( ys 1− y 0)  (4)
 
     As described above, the center coordinates estimating portion  71  determines the center CF of the forward-field-of-view image portion FVa and the center CS of the lateral-field-of-view image portion SVa, and the displacement amount calculating portion  72  can calculate the amounts of displacement from the coordinates of the center CF of the forward-field-of-view image portion FVa and the center CS of the lateral-field-of-view image portion SVa determined by the center coordinates estimating portion  71 . 
     The control portion  60  writes the calculated displacement amount data into the memory  70  and the register  69 . 
     As a result, after manufacture of the endoscope  2  or at time of using the endoscope  2  for the first time, the video processor  32  can read out the displacement amount data from the memory  70  if the endoscope system  1  has been powered on and the center coordinates estimating portion  71  has operated before, and, therefore, the control portion  60  writes the read-out displacement amount data to the register  69 . That is, until a positional relationship detection signal is updated, the boundary correcting portion  66  generates an image signal in which arrangement of the forward-field-of-view image FV and the lateral-field-of-view image is changed based on positional relationship detection information stored in the memory  70 . 
     Further, if the endoscope system  1  has not been powered on, and the center coordinates estimating portion  71  has not operated after manufacture of the endoscope  2 , the control portion  60  cannot read out the displacement amount data from the memory  70  when the endoscope system  1  is powered on. In such a case, the control portion  60  causes the center coordinates estimating portion  71  and the displacement amount calculating portion  72  to operate to perform calculation of the equations (1) to (4) described above, calculates the displacement amount data Dfx, Dfy, Dsx and Dsy, stores the displacement amount data Dfx, Dfy, Dsx and Dsy into the memory  70  and writes the displacement amount data Dfx, Dfy, Dsx and Dsy to the register  69 . 
     As described above, the displacement amount data Dfx, Dfy, Dsx and Dsy are information indicating a positional relationship between the forward-field-of-view image portion FVa and the lateral-field-of-view image portion SVa. The memory  70  is a storage portion configured to store positional relationship detection information. 
     Therefore, the positional displacement correcting portion  65  constitutes an object image position detecting portion configured to detect a positional relationship between the forward-field-of-view image portion FVa, which is a first portion where a front-direction object image is formed, and the lateral-field-of-view image portion SVa, which is a second portion where a lateral-direction object image is formed, in the image pickup device  40  configured to pick up a forward object image and a lateral object image and generate positional relationship detection information. 
     Here, the positional relationship is indicated by the amount of displacement of the portion FVa relative to the center C of the image pickup surface  40   a , which is a predetermined position of an image acquired by the image pickup device  40 , and the amount of displacement of the portion SVa relative to the center C of the image pickup surface  40   a . Therefore, the positional relationship detection information includes the two amounts of displacement. 
     The displacement amount calculating portion  72  executes the displacement amount calculation process described above and outputs a video signal to the cutting out portion  73 . 
       FIG. 9  is a diagram for illustrating a process by the cutting out portion  73 , the enlarging portion  74  and the combining portion  67 . 
     The cutting out portion  73  cuts out the forward-field-of-view image FV and the lateral-field-of-view image SV from the inputted video signal based on the displacement amount data Dfx, Dfy, Dsx and Dsy, and, furthermore, cuts out a central part image FVc with a predetermined radius rp from the forward-field-of-view image FV as shown in  FIG. 9 . As a result, an image of a circumferential part of the forward-field-of-view image FV is not used for an observed image. 
     The enlarging portion  74  enlarges the central part image FVc at a predetermined magnification mr to generate an enlarged central part image FVe. The magnification mr is of such a value that a radius of the enlarged central part image FVe which has been enlarged is larger than a diameter of the forward-field-of-view image FV cut out by the cutting out portion  73 . 
     The combining portion  67  combines the enlarged central part image FVe and the lateral-field-of-view image SV, performs necessary mask processing, and outputs an image to the image outputting portion  68 . 
     As a result, an observed image  50  obtained by the combination becomes an image in which an inside peripheral portion of the lateral-field-of-view image SV is covered and hidden by the enlarged central part image FVe, and a boundary area between the forward-field-of-view image FV and the lateral-field-of-view image SV becomes a smooth image area in the observed image  50  obtained by combination. 
     Therefore, the boundary correcting portion  66  constitutes an image signal generating portion configured to generate an image signal in which the forward-field-of-view image FV and the lateral-field-of-view image SV are arranged with the center CF, which is a reference position provided in the forward-field-of-view image portion FVa, and the center CS, which is a reference position provided in the lateral-field-of-view image portion SVa, caused to correspond to each other, by image processing based on the positional relationship detection information. 
     Note that, though the boundary correcting portion  66  causes positions of the forward-field-of-view image FV and the lateral-field-of-view image SV to change so that both of the center position of the object image in the forward-field-of-view image portion FVa and the center position of the object image in the lateral-field-of-view image portion SVa correspond to the center C of the image pickup surface  40   a  here, the boundary correcting portion  66  may perform a process for causing the position of at least one of the forward-field-of-view image FV and the lateral-field-of-view image SV to change so as to correct displacement between coordinates of the center position of the object image in the forward-field-of-view image portion FVa and coordinates of the center position of the object image in the lateral-field-of-view image portion SVa. In that case, the boundary correcting portion  66  causes arrangement of one of the forward-field-of-view image portion FVa and the lateral-field-of-view image portion SVa to change in accordance with the position of the other between the forward-field-of-view image portion FVa and the lateral-field-of-view image portion SVa, based on the positional relationship detection information indicating a position relationship between the forward-field-of-view image portion FVa and the lateral-field-of-view image portion SVa. 
     Furthermore, note that coordinates of the center position of the object image may be coordinates of a pixel on the monitor  35 , which is a display portion where the forward-field-of-view image FV and the lateral-field-of-view image SV are displayed, and the amount of displacement may be converted to and indicated by the number of pixels on the coordinates. 
     Note that, since sizes of the forward-field-of-view image FV and the lateral-field-of-view image SV differ for each endoscope  2 , information about the predetermined radius rp and the predetermined magnification mr may be stored in the memory  70  of the endoscope  2  in advance, or the control portion  60  may read out the information from the memory  70  and store the information into the register  69  when the endoscope  2  is connected to the video processor  32  and powered on. The boundary correcting portion  66  reads out the information about the predetermined radius rp and the predetermined magnification mr from the register  69  and performs cut-out and enlargement of the central part image FVc. As a result, the boundary between the forward-field-of-view image FV and the lateral-field-of-view image SV becomes inconspicuous in the observed image  50  displayed on the monitor  35 . 
     Note that common smoothing processing may be performed for the boundary area between the combined forward-field-of-view image FV and lateral-field-of-view image SV. 
     As described above, when the endoscope  2  is connected to the video processor  32 , and a process by the positional displacement correcting portion  65  is executed once, displacement amount data is stored into the memory  70 . After that, when the endoscope  2  and the video processor  32  are connected and powered on, the process by the positional displacement correcting portion  65  is not executed, and the control portion  60  reads out the displacement amount data from the memory  70 , and the boundary correcting portion  66  performs boundary correction based on the displacement amount data which has been read out and stored into the register  69 . 
     The process by the positional displacement correcting portion  65  may be executed when the endoscope  2  is manufactured. Even if the process is not executed at the time of manufacture, the process is executed when the endoscope  2  is connected to the video processor  32  for the first time. 
     Furthermore, the process by the positional displacement correcting portion  65  may be adapted to be executed when the endoscope  2  is repaired. 
     As described above, according to the embodiment described above, it is possible to provide an endoscope system which, even if a displacement between optical systems for a forward-field-of-view image FV and a lateral-field-of-view image SV exists due to variation and the like in the processing accuracy of or at the time of assembly of the frame for fixing the lens of the objective optical system or the image pickup device, does not cause the user to feel unnatural from the forward-field-of-view image FV and the lateral-field-of-view image SV simultaneously displayed on the monitor  35 . 
     Furthermore, since centers of the forward-field-of-view image FV and the lateral-field-of-view image SV correspond to each other, a boundary correction process can be performed accurately. 
     Second Embodiment 
     The endoscope system  1  of the first embodiment has the endoscope  2  which obtains a forward-field-of-view image and a lateral-field-of-view image arranged surrounding the forward-field-of-view image with one image pickup device. An endoscope system  1 A of a second embodiment, however, has an endoscope  2 A which obtains a forward-field-of-view image and a lateral-field-of-view image with separate image pickup devices. 
     Note that a configuration of the endoscope system  1 A of the second embodiment is substantially same as the endoscope system  1  described in the first embodiment and shown in  FIG. 1 . Same components will be given same reference numerals, and description of the components will be omitted. 
     (System Configuration) 
       FIG. 10  is a simplified schematic perspective view of the distal end portion  6  of the endoscope  2 A of the present embodiment.  FIG. 11  is a schematic configuration diagram showing an internal configuration of the distal end portion  6 . In  FIGS. 10 and 11 , components such as a treatment instrument opening and cleaning nozzles are omitted. 
     As shown in  FIG. 11 , an image pickup unit  51 A for forward field of view is provided on the distal end face of the cylindrical-shaped distal end portion  6  of the endoscope  2 A. On a side face of the distal end portion  6  of the endoscope  2 A, two image pickup units  51 B and  51 C for lateral field of view are provided. The three image pickup units  51 A,  51 B and  51 C have image pickup devices  40 A,  40 B and  40 C, respectively, and each image pickup unit is provided with an objective optical system not shown. 
     The respective image pickup units  51 A,  51 B and  51 C are arranged on back face sides of a forward observation window  12 A and lateral observation windows  13 A and  13 B, respectively. The image pickup units  51 A,  51 B and  51 C receive reflected light from an object illuminated by illuminating light emitted from two illuminating windows  55 A, two illuminating windows  56 A and two illuminating windows  56 B and output image pickup signals. 
     The three image pickup signals from the three image pickup devices  40 A,  40 B and  40 C are inputted to an A/D conversion portion  61 A ( FIG. 12 ) to be described later. 
     The forward observation window  12 A is arranged on the distal end portion  6  of the insertion portion  4 , facing the direction in which the insertion portion  4  is inserted. The lateral observation windows  13 A and  13 B are arranged on a side face portion of the insertion portion  4  at substantially equal angles in the circumferential direction of the distal end portion  6 , facing the outer diameter direction of the insertion portion  4 . The lateral observation windows  13 A and  13 B are arranged on the distal end portion  6  so as to face mutually opposite directions. 
     The image pickup devices  40 A,  40 B and  40 C of the image pickup units  51 A,  51 B and  51 C are electrically connected to the video processor  32 A ( FIG. 12 ) and controlled by the video processor  32 A to output image pickup signals to the video processor  32 A. Each of the image pickup units  51 A,  51 B and  51 C is an image pickup portion configured to photoelectrically convert an object image. 
     That is, the forward observation window  12 A is provided on the insertion portion  4  and constitutes a first image acquiring portion configured to acquire an image of a first object image from a forward direction, which is a first direction, and each of the lateral observation windows  13 A and  13 B is provided on the insertion portion  4  and constitutes a second image acquiring portion configured to acquire a second object image from a lateral direction, which is a second direction different from the forward direction. In other words, the first object image is an object image in the first direction including the forward direction of the insertion portion substantially parallel to the longitudinal direction of the insertion portion  4 , and the second object image is an object image in the second direction including the lateral direction of the insertion portion substantially orthogonal to the longitudinal direction of the insertion portion  4 . Furthermore, the forward observation window  12 A is a forward image acquiring portion configured to acquire an object image in a direction including the forward direction of the insertion portion, and the lateral observation windows  13 A and  13 B are lateral image acquiring portions configured to acquire an object image in a direction including the lateral direction of the insertion portion. 
     The image pickup unit  51 A is an image pickup portion configured to photoelectrically convert an image from the forward observation window  12 A, and the image pickup units  51 B and  51 C are image pickup portions configured to photoelectrically convert two images from the lateral observation windows  13 A and  13 B, respectively. That is, the image pickup unit  51 A is an image pickup portion configured to pick up an object image for acquiring a forward-field-of-view image, and the image pickup units  51 B and  51 C are image pickup portions configured to pick up an object image for acquiring a lateral-field-of-view image, respectively. An image signal of the forward-field-of-view image is generated from an image obtained by the image pickup unit  51 A, and image signals of the two lateral-field-of-view images are generated from images obtained by the image pickup units  51 B and  51 C. 
     On a back side of each of the illuminating windows  55 A,  56 A and  56 B, a distal end portion of a light guide not shown or a luminous body such as a light emitting diode (LED) is arranged in the distal end portion  6 . 
     (Configuration of Video Processor) 
       FIG. 12  is a block diagram showing a configuration of the video processor  32 A according to the present embodiment. Note that, in  FIG. 12 , only components related to functions of the present embodiment described below are shown, and components related to other functions such as image recording are omitted. Further, in the configuration of the video processor  32 A of  FIG. 12 , same components as components of the video processor  32  of the first embodiment will be given same reference numerals, and description of the components will be omitted. 
     As shown in  FIG. 12 , the video processor  32 A has the control portion  60 , the A/D conversion portion  61 A, a positional displacement correcting portion  65 A, a boundary correcting portion  66 A, a combining portion  67 A, the preprocessing portion  62 , a light-adjusting portion  63 A, an enlarging/reducing portion  64 A, the image outputting portion  68 , and the register  69 . 
     The A/D conversion portion  61 A includes three A/D conversion circuits. The respective A/D conversion circuits are circuits configured to convert image pickup signals from the respective image pickup devices  40 A,  40 B and  40 C of the endoscope  2 A from analog signals to digital signals. 
     The positional displacement correcting portion  65 A has the center coordinates estimating portion  71  and the displacement amount calculating portion  72  shown in  FIG. 7  and executes a process for calculating an amount of displacement of each of three images obtained by the three image pickup devices  40 A,  40 B and  40 C. The positional displacement correcting portion  65 A stores three pieces of displacement amount data calculated for the three image pickup devices  40 A,  40 B and  40 C into the memory  70  of the endoscope  2  as well as into the register  69 . 
     The positional displacement correcting portion  65 A outputs video signals of the three inputted images to the boundary correcting portion  66 A. 
     The boundary correcting portion  66 A has the cutting out portion  73  and the enlarging portion  74  shown in  FIG. 7 , and executes an image cut-out process and a predetermined enlargement process for each of the inputted video signal using the three pieces of displacement amount data stored in the register  69 . 
     The combining portion  67 A combines three endoscopic images in order to arrange and display the endoscopic images on a screen of the monitor  35  and outputs an image obtained by the combination to the preprocessing portion  62 . 
     Note that, though one monitor  35  is provided in the present embodiment, a forward-field-of-view image and two lateral-field-of-view images may be displayed on separate monitors, respectively. In such a case, the combining portion  67 A is unnecessary. 
     The light-adjusting portion  63 A is a circuit configured to judge brightness of each of images in the video signals received from the preprocessing portion  62  and output a light adjustment control signal to the light source apparatus  31  based on a light adjustment state of the light source apparatus  31 . 
     The enlarging/reducing portion  64 A enlarges or reduces the images of the video signals from the preprocessing portion  62  in accordance with the size and format of the monitor  35 , and outputs video signals of the enlarged or reduced images to the image outputting portion  68 . 
       FIG. 13  is a diagram showing an example of an observed image displayed on the monitor  35  by image processing by the video processor  32 A of the endoscope system  1 A. 
     As shown in  FIG. 13 , an observed image  50 A, which is an endoscopic image displayed on the display screen  35   a  of the monitor  35 , includes three image display portions  81 ,  82  and  83 . Each of the image display portions  81 ,  82  and  83  is a substantially rectangular image. A forward-field-of-view image FV is displayed at a center; a right-side lateral-field-of-view image SV 1  is displayed on a right side; and a left-side lateral-field-of-view image SV 2  is displayed on a left side. That is, the image outputting portion  68  causes the two lateral-field-of-view images SV 1  and SV 2  to be displayed on the monitor  35 , which is a display portion, so that the lateral-field-of-view images SV 1  and SV 2  are positioned next to the forward-field-of-view image FV. 
     The plurality of lateral-field-of-view images exist. Here, at least on both sides of the forward-field-of-view image FV, a plurality of lateral-field-of-view images, here, the two lateral-field-of-view images SV 1  and SV 2  are arranged. 
     The forward-field-of-view image FV is generated from an image acquired by the image pickup device  40 A ( FIG. 11 ) of the image pickup unit  51 A. The image of the image display portion  82  is generated from an image acquired by the image pickup device  40 B ( FIG. 11 ) of the image pickup unit  51 B. The image of the image display portion  83  is generated from an image acquired by the image pickup device  40 C ( FIG. 11 ) of the image pickup unit  51 C. 
     (Operation) 
     Next, description will be made on an example of a procedure about a method for a process for correcting a positional displacement among the forward-field-of-view image FV and the two lateral-field-of-view images SV 1  and SV 2  in the video processor  32 A. 
     In the case of the present embodiment, the image pickup unit  51 A and the two image pickup units  51 B and  51 C are arranged on the distal end portion  6  so that the image pickup unit  51 A picks up an image of the forward direction of the distal end portion  6 , and the image pickup units  51 B and  51 C pick up images of the lateral direction of the distal end portion  6  in mutually opposite directions. Therefore, in some cases, each of central axes of the three image pickup devices  40 A,  40 B and  40 C is displaced relative to a predetermined optical axis in a horizontal or vertical direction due to variation and the like in processing accuracy of or at time of assembly of a frame for fixing each lens of objective optical systems or each of the image pickup devices  40 A,  40 B and  40 C of the respective image pickup units  51 A,  51 B and  51 C. 
     Therefore, in the present embodiment, the positional displacement correcting portion  65 A configured to execute a positional displacement correction process calculates, for the three images, an amount of displacement from a predetermined position by image processing. 
     In the present embodiment also, the positional displacement correcting portion  65 A is controlled by the control portion  60  so as to operate when the endoscope  2 A is connected to the video processor  32 A and powered on, at manufacture of the endoscope  2 A or at time of using the endoscope  2 A for the first time, similarly to the first embodiment. 
     At that time, the positional displacement correction process is caused to be executed in a state that a predetermined cap  91  is put on the distal end portion  6 . 
       FIG. 14  is a perspective view showing a configuration of the cap  91 . 
     The cap  91  is a member having a cylindrical shape with a distal end portion closed. The cap  91  has an opening  91   a  through which the distal end portion  6  of the insertion portion  4  can be inserted from a proximal end side of the cap  91 . 
     On an internal wall surface  92  and an internal circumferential surface  93  on a distal end side of the cap  91 , predetermined reference figures are provided by printing or the like. 
     Here, the reference image provided on the internal wall surface  92  on the distal end side of the cap  91  is cross lines  94  extending in an upward-and-downward direction and a left-and-right direction, respectively. The reference image provided on the internal circumferential surface  93  of the cap  91  is grid lines  95  extending in the upward-and-downward direction and the left-and-right direction, respectively. 
     As shown by a two-dot chain line arrow A, the user inserts the distal end portion  6  into the cap  91  from the opening  91   a , puts the cap  91  on the distal end portion  6 , and then causes the positional displacement correcting portion  65 A to operate. 
     Note that, in order that each of the image pickup devices  40 A,  40 B and  40 C picks up an image of the cross lines  94  and the grid lines  95  in the cap  91  around an axis of the distal end portion  6  at a predetermined angle, reference position marks (not shown) or the like for positioning are provided on the cap  91  and the distal end portion  6 . 
     That is, in a state that the cap  91  is put on the distal end portion  6  with the reference position marks (not shown) on the cap  91  and the distal end portion  6  aligned with each other, a vertical direction of the image pickup device  40 A and a direction of a vertical line of the cross lines  94  correspond to each other, and a horizontal direction of the image pickup device  40 A and a direction of a horizontal line of the cross lines  94  correspond to each other in an image obtained when the image pickup device  40 A picks up an image of the cross lines  94  in the cap  91 . 
     In a state that the cap  91  is put on the distal end portion  6  with the reference position marks (not shown) on the cap  91  and the distal end portion  6  aligned with each other, each of vertical directions of the image pickup devices  40 B and  40 C and a direction of a vertical line of the grid lines  95  correspond to each other in the image obtained when the image pickup device  40 A picks up an image of the cross lines  94  in the cap  91 . 
       FIG. 15  is a diagram for illustrating displacements of object images formed on image pickup surfaces of the respective image pickup devices  40 A,  40 B and  40 C. In  FIG. 15 , areas  40 AI,  40 BI and  40 CI indicate ranges of images obtained on the image pickup surfaces of the image pickup devices  40 A,  40 B and  40 C, respectively. 
     The image obtained by each image pickup device is obtained by cutting out an area with a predetermined size in an image pickup signal of the image pickup device. A reference point for cut-out is a center point of each image (hereinafter referred to as an image center point). 
     A predetermined area is cut out from the area  40 AI obtained by the image pickup device  40 A with an image center point CC as a reference; a predetermined area is cut out from the area  40 BI obtained by the image pickup device  40 B with an image center point CR as a reference; and a predetermined area is cut out from the area  40 CI obtained by the image pickup device  40 C with an image center point CL as a reference. 
     At time of the positional displacement correction process, an image of the cross lines  94  provided on the internal wall surface  92  on the distal end side of the cap  91  is included in the area  40 AI obtained by the image pickup device  40 A. An image of the grid lines  95  provided on the internal circumferential surface  93  in the cap  91  is included in the areas  40 BI and  40 CI obtained by the image pickup devices  40 B and  40 C. 
     If the processing accuracy of the frame for fixing each lens of the objective optical system or each image pickup device of each image pickup unit is complete, and does not have variation and the like at the time of assembly, the image center point CC corresponds to an intersection point CP as a center point of the cross lines  94  in the area  40 AI. Furthermore, the image center points CR and CL of the image pickup devices  40 B and  40 C correspond to center points GR and GL of the grid lines  95 , respectively. 
     As shown in  FIG. 15 , however, though the vertical line and horizontal line of the cross lines  94  are parallel to a Y direction and an X direction, respectively, in the area  40 AI obtained by the image pickup device  40 A, the image center point CC passing through the central axis of the image pickup device  40 A and the intersection point CP as the center point of the cross lines  94  do not correspond to each other if variation and the like in the processing accuracy of or at the time of assembly of the frame for fixing each lens of the objective optical system or the image pickup device of each image pickup unit exist. 
     In the area  40 BI obtained by the image pickup device  40 B also, though the vertical line and horizontal line of the grid lines  95  are parallel to the Y direction and the X direction, respectively, the image center point CR passing through a central axis of the image pickup device  40 B and the center point GR of the grid lines  95  do not correspond to each other for a similar reason. In the image obtained by the image pickup device  40 C also, though the vertical line and horizontal line of the grid lines  95  are parallel to the Y direction and the X direction, respectively, the image center point CL passing through a central axis of the image pickup device  40 C and the center point GL of the grid lines  95  do not correspond to each other for a similar reason. 
     Though the intersection point CP of the cross lines  94 , the points GR and GL at the center on the horizontal line between the two vertical lines of the grid lines  95 , and the respective image center points CC, CR and CL are used to determine the amount of displacement here, points at other positions may be used. 
     The center coordinates estimating portion  71  of the positional displacement correcting portion  65 A calculates and estimates the center points of the reference figures (the cross lines  94  and the grid lines  95 ) in each image (hereinafter referred to as reference figure center points). More specifically, the center coordinates estimating portion  71  determines, in the area  40 AI, a position of the intersection point CP of the cross lines  94  on the image pickup surface  40   a , and determines, in the area  40 BI and the image CI, positions of the center points GR and GL of the grid lines  95  on the image pickup surface  40   a , respectively, by image processing. 
     The displacement amount calculating portion  72  calculates an amount of displacement of the reference figure center point relative to the image center point of each image. The control portion  60  stores the calculated displacement amount data into the memory  70  of the endoscope  2 A as well as into the register  69 . 
     The displacement amount data of the reference figure center point relative to the image center point of each image is information showing a positional relationship among the areas  40 AI,  40 BI and  40 CI. More specifically, the positional displacement correcting portion  65 A calculates, for the area  40 AI, an amount of displacement D 1   x  in an X axis direction and an amount of displacement D 1   y  in a Y axis direction between the image center point CC and the reference figure center point CP of the cross lines  94  on the image pickup surface  40   a  of the image pickup device  40 A. 
     Similarly, the positional displacement correcting portion  65 A calculates, for the area  40 BI, an amount of displacement D 2   x  in the X axis direction and an amount of displacement D 2   y  in the Y axis direction between the image center point CR and the reference figure center point GR of the grid lines  95  on the image pickup surface  40   a  of the image pickup device  40 B. 
     Similarly, the positional displacement correcting portion  65 A calculates, for the area  40 CI, an amount of displacement D 3   x  in the X axis direction and an amount of displacement D 3   y  in the Y axis direction between the image center point CL and the reference figure center point GL of the grid lines  95  on the image pickup surface  40   a  of the image pickup device  40 C. 
     Therefore, the positional displacement correcting portion  65  constitutes an object image position detecting portion configured to detect a positional relationship among the area  40 AI where a forward object image is formed, the area  40 BI where a first lateral object image is formed, and the area  40 CI where a second lateral object image is formed, in the image pickup devices  40 A,  40 B and  40 C configured to pick up a forward object image and two lateral object images and generate positional relationship detection information. 
     The boundary correcting portion  66 A cuts out images from the respective images so that the three reference figure center points CP, GR and GL correspond to one another, based on the three pieces of displacement amount data stored in the register  69 , and executes an enlargement process so that the respective images are of a same size. 
     The cutting out portion  73  of the boundary correcting portion  66 A cuts out the respective images, for example, with the reference figure center point CP as a center of image cut-out for the area  40 AI, with the reference figure center point CR as a center of image cut-out for the area  40 BI, and with the reference figure center point CL as a center of image cut-out for the area  40 CI. 
     As a result, in  FIG. 15 , an area indicated by a two-dot chain line is cut out from each of the areas  40 AI, BI and CI. 
     Since in some cases, sizes of the three images cut out by the cutting out portion  73  are different from one another, the enlarging portion  74  of the boundary correcting portion  66 A executes an enlargement process or a reduction process for each of the images so that the sizes of the three images become the same, and outputs the images to the combining portion  67 A. 
     That is, the boundary correcting portion  66 A constitutes an image signal generating portion configured to generate an image signal in which the forward-field-of-view image FV and the two lateral-field-of-view images SV 1  and SV 2  are arranged such that the reference figure center point CP, which is a reference position provided in the area  40 AI, and the reference figure center points GR and GL, which are second reference positions provided in the areas  40 BI and  40 CI, are adjusted to correspond to one another based on the positional relationship detection information. 
     In other words, the boundary correcting portion  66 A generates an image signal in which arrangement of the forward-field-of-view image FV and the two lateral-field-of-view images SV 1  and SV 2  is changed so that coordinates of the reference figure center point CP, which is a reference position provided in the area  40 AI, and coordinates of the reference figure center points GR and GL provided in at least two areas  40 BI and  40 CI, respectively, are adjusted to correspond to one another. 
     Note that, though the boundary correcting portion  66 A causes positions of cutting out the forward-field-of-view image FV and the lateral-field-of-view images SV 1  and SV 2  to change so that the reference figure center points CP, GR and GL of the respective areas  40 AI,  40 BI and  40 CI correspond to one another here, the boundary correcting portion  66 A may perform a process for changing the positions of the forward-field-of-view image FV and at least one of the lateral-field-of-view images SV so that a displacement between a straight line extending in a vertical or horizontal direction from coordinates of a predetermined position of a reference figure in a forward-field-of-view image portion FVa and a straight line extending in the vertical or horizontal direction from coordinates of a predetermined position of a reference figure in a lateral-field-of-view image portion SVa is corrected in each of the areas  40 AI,  40 BI and  40 CI. In that case, the boundary correcting portion  66 A causes arrangement of two among the three areas to change in accordance with the position of the other one area based on the positional relationship detection information showing the positional relationship among respective areas  40 AI,  40 BI and  40 CI. 
     Furthermore, note that the coordinates of each reference image may be coordinates of a pixel on the monitor  35 , which is a display portion where the forward-field-of-view image FV and the lateral-field-of-view images SV 1  and SV 2  are displayed, and the amount of displacement may be converted to and indicated by the number of pixels on the coordinates. 
       FIG. 16  is a diagram for illustrating an example in which positional displacement correction according to the present embodiment has been performed. 
     In  FIG. 16 , an upper part shows the three respective areas  40 AI,  40 BI and  40 CI, and the image center point in each of the areas  40 AI,  40 BI and  40 CI is displaced relative to a predetermined position in a case where no variation and the like in the processing accuracy or at the time of assembly exists. 
     By performing the positional displacement correction process as described above, however, the cut out areas are changed, and three endoscopic images are displayed on the monitor  35  as shown in a lower part, so that the user can see the three endoscopic images without feeling unnatural. 
     Note that, though lateral-direction positional displacement adjustment is performed based on an amount of displacement of a reference figure center point relative to an image center point in each of the areas  40 AI,  40 BI and  40 CI, the lateral-direction positional displacement adjustment may be performed so that a distance from the reference figure center point CP in the image display portion  81  to the reference figure center point CR in the image display portion  82  and a distance from the reference figure center point CP in the image display portion  81  to the reference figure center point CL in the image display portion  83  on the display screen  35   a  may be equal. 
     In the present embodiment also, the control portion  60  reads out data from the memory  70  of the endoscope  2  to judge whether displacement amount data exists or not. If the displacement amount data is not stored in the memory  70 , the control portion  60  causes the center coordinates estimating portion  71  and the displacement amount calculating portion  72  to operate and performs control to execute the positional displacement correction process. 
     Note that, in the present embodiment also, the process by the positional displacement correcting portion  65  may be adapted to be executed when the endoscope  2  is repaired. 
     Furthermore, note that, though the mechanism configured to realize the function of illuminating and observing the lateral direction is included in the insertion portion  4  together with the mechanism configured to realize the function of illuminating and observing the forward direction in the second embodiment described above, the mechanism configured to realize the function of illuminating and observing the lateral direction may be a separate body attachable to and detachable from the insertion portion  4 . 
       FIG. 17  is a perspective view of a distal end portion  6   a  of the insertion portion  4  to which a unit for lateral observation is fitted, according to a modification of the second embodiment. The distal end portion  6   a  of the insertion portion  4  has a forward-field-of-view unit  600 . A lateral-field-of-view unit  500  has a configuration of being attachable to and detachable from the forward-field-of-view unit  600  by a clip portion  501 . 
     The forward-field-of-view unit  600  has the forward observation window  12 A for acquiring a forward-field-of-view image FV and an illuminating window  601  for illuminating the forward direction. The lateral-field-of-view unit  500  has the two lateral observation windows  13 A and  13 B for acquiring images in the left-and-right direction and two illuminating windows  502  for illuminating the left-and-right direction. 
     The video processor  32 A and the like can perform acquisition and display of an observed image as shown in the embodiments described above by lighting up and lighting out each illuminating window  502  of the lateral-field-of-view unit  500  in accordance with a frame rate of a forward field of view. 
     As described above, according to the embodiment described above, it is possible to provide an endoscope system which, even if a displacement between optical systems for a forward-field-of-view image FV and a lateral-field-of-view image SV exists due to variation and the like in the processing accuracy of or at the time of assembly of the frame for fixing the lens of the objective optical system or the image pickup device, does not cause the user to feel unnatural from the forward-field-of-view image FV and the two lateral-field-of-view images SV 1  and SV 2  simultaneously displayed on the monitor  35 , and an image processing method. 
     The present invention is not limited to the embodiments described above, and various changes, alterations and the like are possible within a range not changing the spirit of the present invention.