hereinafter , the preferred embodiments of the present invention are described with reference to the attached drawings . fig1 is a block diagram of an electronic endoscope according to the first embodiment . the electronic endoscope has a video - scope 50 with a ccd 54 , and a video - processor 10 that has a lamp 12 and processes image - pixel signals read from the ccd 54 . the video - scope 50 is detachably connected to the video - processor 10 ; and a monitor 52 and a recorder 53 that records a still image are connected to the video - processor 10 . when a lamp switch button ( not shown ) is turned on , a lamp controller 11 supplies electric power to the lamp 12 so that the lamp 12 radiates illuminating light . light emitted from the lamp 12 enters the incidence surface 51 a of a light - guide 51 via a rotary shutter 15 and a collecting lens 16 . the light - guide 51 is constructed of a fiber - optic bundle for directing the light to a tip end of the video - scope 10 . the light exits from the end portion 51 b of the light - guide 51 , and illuminates an observed object via a diffusion lens ( not shown ). light , reflected on the object , reaches the ccd 54 via an objective lens ( not shown ), so that an object image is formed on the photo - sensitive area of the ccd 54 . a color filter , checkered by four color elements of yellow ( y ), magenta ( m ), cyan ( c ), and green ( g ), is arranged on the photo - receiving area such that the four color elements are opposite to pixels arranged in the photo - sensitive area . based on the light passing through each color element , analog image - pixel signals are generated by the photoelectric transformation effect . the generated image - pixel signals are read from the ccd 54 at regular time intervals in accordance with clock pulse signals output from a ccd driver 54 . a timing control circuit 58 in the video - scope 50 adjusts an output - timing of the clock pulse signals . the ccd 54 is an interline - transfer ccd , and as for the color imaging method using an on - chip color filter , the so called “ color difference lines sequential system ” is applied . therefore , while displaying a movie image , the photo - generated charges in pixels neighboring each other are mixed , and odd - field image - pixel signals and even - field image - pixel signals are alternately read from the ccd 54 . the ntsc ( or pal ) standard is herein applied as the tv standard , accordingly , the odd or even field image - pixel signals are read from the ccd 54 at a 1 / 60 ( or 1 / 50 ) second time interval , and are then fed to an amplifier 55 . the image - pixel signals are amplified in the amplifier 55 and are subjected to given processes in a first signal processing circuit 57 . the processed image - pixel signals are fed to a second signal processing circuit 28 . in the second signal processing circuit 28 , various processes , such a gamma correction process , a white balance process , and soon , are carried out on the image - pixel signals , so that digital image signals are generated and temporarily stored in an image memory 29 as digital image data . the digital image signals are read from the image memory and video signals such as ntsc signals are output to the monitor 52 at a given timing , thus an observed image is displayed on the monitor 52 as a movie image . on the other hand , when displaying a still image on the monitor 52 and recording the still image in the recorder 53 by depressing a freeze button 53 a on the video - scope 50 , a one - time reading process , wherein one frame worth of image - pixel signals is generated by a one - time exposure , is performed . when electric charges are accumulated by a one - time exposure , image - pixel signals corresponding to an odd - line in the pixel - array are read from the ccd 54 over one - field reading interval , next , image - pixel signals corresponding to an even - line in the pixel array are read from the ccd 54 over one - field reading interval . one field worth of odd - line image - pixel signals and one field worth of even - line image - pixel signals are respectively fed to the amplifier 55 , the first signal processing circuit 57 , and the second signal processing circuit 28 . then , odd - field image signals and even - field image signals are respectively output to the monitor 52 . also , one field worth of odd - line image - pixel signals and one field worth of even - line image - pixel signals , which are processed in the second signal processing circuit 28 , are fed to the recorder 53 as still image data . a system control circuit 22 including a cpu ( not shown ) controls each circuit in the video - processor 10 , and outputs control signals to the lamp controller 11 , the second signal processing circuit 28 , and so on . a timing control circuit , provided in the video - processor 10 ( not shown ), outputs clock pulse signals to each circuit in the video - processor 10 to adjust a process - timing , and outputs synchronous signals which are added to the video signals , to the second signal processing circuit 28 . the system control circuit 22 controls an output - timing of the clock pulse signals fed to each circuit . for example , the system control circuit 22 adjusts an output - timing of clock pulse signals , which are output to the image memory 28 in accordance with the operation of the freeze button 53 a to renew or rewrite image data , and adjusts an output - timing of clock pulse signals , which are output from the ccd driver 59 to drive the ccd 54 . a scope controller 56 , provided in the video - scope 50 , controls the first signal processing circuit 55 and the timing control circuit 58 . the timing control circuit 58 outputs driving signals to the ccd driver 59 in accordance with the control signals output from the scope controller 56 . thus , the reading process of the image - pixel signals is controlled . when the video - scope 50 is connected to the video - processor 10 , data are transmitted between the video - scope 50 and the video - processor 10 . the rotary shutter 15 is attached to a motor ( not shown ), and rotates at a constant speed on the basis of driving signals fed from a motor driver 23 . a chopper 17 , which shades or blocks the light to be directed to the end portion of the video - scope 50 , is provided between the rotary shutter 15 and the collecting lens 16 , and has a dc solenoid ( herein , not shown ). the chopper 17 motions in accordance with a series of pulse signals fed from a pwm driving circuit 24 . fig2 is a plan view of the rotary shutter 15 . fig3 is a plan view of the chopper 17 . the rotary shutter 15 is constructed of an aperture 15 a that passes the light from the lamp 12 and a shading portion 15 b that shades or shields the light . the aperture 15 a is formed such that a pair of arc - shaped holes is opposite to each other . the rotary shutter 15 rotates by one - rotation in one - frame reading interval (= 1 / 30 or 1 / 25 second ). therefore , the half - circle 15 p of the rotary shutter 15 corresponds to one - field reading interval (= 1 / 60 or 1 / 50 second ). while the rotary shutter 15 rotates by a half - rotation , the aperture 15 a and shading portion 15 b pass the light - path of the light emitted from the lamp 12 , in turn . thus , an exposure interval and a shading interval alternately occur in one - field reading interval , which functions like an electronic shutter . when displaying and recording the still image , one frame worth of image - pixel signals is obtained by light passing through one aperture 15 a , namely , by rotating the rotary shutter 15 by a half - rotation . then , the obtained one frame worth of image - pixel signals is read from the ccd 54 over the one - frame reading interval (= 1 / 30 or 1 / 25 second ). since the other aperture 15 a passes the light - path for the remaining interval (= 1 / 60 or 1 / 50 second ), the chopper 17 moves so as to block the illuminating light when the other aperture 15 a passes the light - path . in fig3 , the non - shading position of the chopper 17 , which enables light to pass through one arc - shaped hole of the aperture 15 a , is shown by a solid line , whereas the shading position of the chopper 17 , which blocks the light when the other arc - shaped hole of aperture 15 a passes the light - path , is shown by a broken line . the chopper 17 is a pivot - type solenoid , and has a dc solenoid 17 a and a plate member 17 b , which pivots around a center axis 17 c . when the chopper 17 motions so as to shade the illuminating light , an end portion 17 d of the plate member 17 b covers the light - path or the aperture 15 a of the rotary shutter 15 . the pwm driving circuit 24 is a pwm controller , which outputs a sequence of pulse signals to the solenoid 17 a . fig4 is a view showing a timing chart of the recording process . in a state where the freeze button 53 a is not pressed , namely , a movie image is displayed , odd - field image - pixel signals and even - field image - pixel signals are alternately read from the ccd 54 at a 1 / 60 ( or 1 / 50 ) of a second interval while mixing adjacent pixel signals , as described above . since the ccd 54 is an interline type ccd , the photo - generated charges , which are accumulated by a given exposure - timing , are read in the next exposure - timing . for example , image - pixel signals , which are accumulated at “ n − 1 ” of the exposure - timing and correspond to the even - field , are read from the ccd 54 at “ n ” of the exposure - timing , as shown in fig4 . clock pulse signals , which update the image data in the image memory 29 , are output to the image memory 29 at 1 / 60 ( or 1 / 50 ) time interval . when the freeze button 53 a is pressed to start recording a still image , all pixel signals , which are obtained during a one - time exposure time ( in fig4 , the signals in the order of “ n ”), are read from the ccd 54 over a one - frame reading interval . concretely , odd - line image - pixel signals and even - line image - pixel signals are read from the ccd 54 , in turn , over two field intervals . during the reading of all image - pixel signals , the chopper 17 motions to block the illuminating light . further , when the recording process is performed , the output - interval of the clock pulse signals for update is changed from one - field interval to two - field ( one - frame ) intervals . the two - field intervals are based on pulse signals “ sp ”, which are output at an exposure - time just before an exposure - time for recording the still image . consequently , the odd - field image - pixel signals and the even - field image - pixel signals are respectively used to display the observed image over two field intervals . an observed image , formed by the odd - field image - pixel signals , is displayed for 1 / 30 ( or 1 / 25 ) of a second , and an observed image , formed by the even - field image - pixel signals , is also displayed for 1 / 30 ( 1 / 25 ) of a second . after the one frame worth of image - pixel signals ( odd - line image - pixel signals and even - line image - pixel signals ) are read from the ccd 54 , the interval of the update returns to one field interval . with reference to fig5 , the second embodiment is explained . the second embodiment is different from the first embodiment in that image data is not renewed while recording the still image . fig5 is a view showing a timing chart of a recording process according to the second embodiment . when the recording process is started by depressing the freeze button 53 a , as shown in fig5 , clock pulse signals for update are not output to the image memory 29 over two - field intervals . then , odd - field image - pixel signals , obtained by an exposure just before the exposure for recording the still image , are used to display the observed image until the one frame worth of image - pixel signals for the still image is read from the ccd 54 . finally , it will be understood by those skilled in the arts that the foregoing description is of preferred embodiments of the device , and that various changes and modifications may be made to the present invention without departing from the spirit and scope thereof . the present disclosure relates to subject matter contained in japanese patent application no . 2005 - 056979 ( filed on mar . 2 , 2005 ), which is expressly incorporated herein , by reference , in its entirety .
an electronic endoscope has a light source that radiates illuminating light , a movie - image processor , a still - image processor , an image - change processor , and provisional image displayer . the still - image processor that alternately reads odd - line image - pixel signals and even - line image - pixel signals over two field interval to generate a still image on the basis of one frame worth of image - pixel signals generated by a one - time still image exposure . the illuminating light being blocked for a latter filed interval in the two field interval . the image change processor switches between a performance of the movie - image processor for displaying the movie - image and a performance of the still - image processor for displaying the still - image . while the still - image processor reads the odd - line and even - line image - pixel signals over the two field intervals , the provisional image displayer displays a provisional image on the basis of at least one of odd - field image - pixel signals and even - field image - pixel signals , which are obtained by an exposure before the still image exposure .