referring now to fig1 to 9 , preferred embodiments of the present invention will be explained hereinafter . fig1 is a diagram showing a basic configuration of the present invention . in fig1 denotes a light source which is able to provide shutter - cells 11 ar , 11 br respectively associated with the right eyes of viewers 15 a , 15 b and shutter - cells 11 al , 11 bl respectively associated with the left eyes of viewers 15 a , 15 b . the light source 11 can be achieved by providing a light source and an lcd shutter panel in front of the light source , wherein the shutter panel is able to control its light transmission and blocking positions , as will be described in detail in reference to fig2 later . lights from the light source 11 pass through a convex lens 12 and then focuses on the right eyes and the left eyes of the viewers . the lights passing through the convex lens 12 again pass through an lcd spatial modulator 18 . the lcd spatial modulator 13 displays an image associated with the viewer &# 39 ; s right eye when the light source 11 emits lights associated with the right eyes , and it display the image associated with the viewer &# 39 ; s left eye when the light source 11 emits lights associated with the left eyes . in the drawing solid lines represent light paths for providing a stereoscopic view to the viewer 15 b , while dotted lines represent light paths for providing a stereoscopic view to the viewer 15 a . a tracker / interface 14 determines the stereoscopic image display or the normal plane image display in accordance with the position of the viewer or his / her instruction . when the viewer 15 a tilts his / her head , and then it is difficult to fuse the right and left stereoscopic images with each other or to provide the viewer 15 a with a stereoscopic view , the tracker / interface 14 recognizes the condition and provides information as a result if the recognition to the controller 16 . then the controller 16 controls the light source 11 so as to designate shutter - cells for presenting the viewer 15 a with a normal plane image display . that is , it operates to provide the normal plane image display to the viewer 15 a . there are a various ways of presenting such normal plane image display as described later . fig2 is a diagram showing a preferred embodiment of the stereoscopic image display apparatus according to the present invention . the stereoscopic image display , as shown in fig2 is characterized by that it is provided with an lcd spatial modulator 25 as the spatial modulator for alternatively displaying the right and the left images . in the stereoscopic image display apparatus of the embodiment , as shown in fig2 the optical source 11 is comprised of an optical source 21 , a diffuser panel 22 and an lcd shutter panel 23 . 24 denotes a convex lens , 25 denotes an lcd spatial modulator , and 26 a and 26 b denote viewers , respectively . the tracker / interface 14 is comprised of a camera 27 , an eye - tracker 28 and a receiver 29 for receiving a remote control signal from a remote controller 16 operable by the viewers . the controller 16 is comprised of a light - cell designator 30 , and a light source controller 31 . 32 is an lcd spatial modulator controller , which supplies the right image signal and the left image signal in turn to the lcd spatial modulator 25 . the supply timing signal is applied also to the light source controller 31 of the controller 16 . the light from the light source 21 becomes the diffusion light thorough the diffuser panel 22 and input to the lcd shutter panel 23 . on the lcd shutter panel 23 , in fig4 a and 4 b shutter - cells 23 al , 23 ar , 23 bl and 23 br are defined . the shutter - cells 23 al 23 ar are addressed to the viewer 26 a , while the shutter - cells 23 bl , 23 br are addressed to the viewer 26 b . the shutter - cells are controlled by the light source controller 31 , the diffusion light passes through the shutter - cells . the positions of the shutter - cells 23 al , 23 ar , 23 bl and 23 br are associated with the left and right eyes of the viewers 26 a and 26 b in a one - to - one relationship . when the number of the viewers changes , the designation of the shutter - cell associated with the viewer &# 39 ; s eyes are controlled in accordance with the increase or decrease of the viewers . the location information of the viewer is fed back as the position of the shutter - cell . in one embodiment , the eye - tracker 28 tracks the eye movement of the viewers based on the pictures of the viewers taken by camera 27 . the eye - position information obtained by the eye - tracker 28 is transferred to the light - cell designator 30 . the light - cell designator 30 sets up the position of the shutter - cell associated with the eyes of the viewer based on the eye - position information . the set up result is sent to the light pass / block controller 31 . accordingly , the shutter - cell position of the lcd shutter panel 23 is decided . then , the lights passing through the shutter - cells 23 al , 23 ar , 23 bl , and 23 br are focused around the eyes of the viewers 26 a , 26 b by the convex lens positioned between the convex lens 23 and the viewers 26 a , 26 b , is a lcd spatial modulator 25 for alternatively displaying the right and the left images which are output by the panel control apparatus 32 , so that the viewers 26 a , 26 b can observe the stereoscopic image , i . e ., the alternately displayed right and left images . the control operation of the shutter - cells 23 al , 23 ar for presenting the stereoscopic image to the viewer 26 a ( hereafter the operation will be referred to as a 3d mode operation ) will be explained in reference to fig2 and 3 . fig3 a is a timing chart of the right and left images with a parallax therebetween , alternately projected on the lcd spatial modulator 25 . fig3 b is a timing chart showing the open / close operation of the shutter - cell 23 al , 23 ar associated with the right and left eyes in the 3d mode operation . as seen from fig3 a to 3 c , when the image for right eye is displayed on the lcd spatial modulator 25 , the shutter - cell 23 ar associated with the right eye is activated while the shutter - cell 23 al associated wit the left eye is deactivated . when the image for the left eye is displayed on the lcd spatial modulator 25 , the shutter - cell 23 ar associated with the right eye is deactivated , while the shutter - cell 23 al associated with the left eye is activated . accordingly , the viewer can observe the display image as the stereoscopic image by using parallax . now , the open / close operation of the shutter - cell in the normal plane image display mode ( hereafter the operation will be referred to as a 2d mode operation ) will be explained . fig3 c is timing chart showing the shutter - cell open / close operation in the 2d mode operation . when the image for the right eye is displayed on the lcd spatial modulator 25 , both the shutter - cells 23 al , 23 ar associated with both right and left eyes are activated . when the image for left eye is displayed both the shutter - cells 23 al , 23 ar associated with both right and left eyes are closed . accordingly , the viewer observe the image for the right eye among the display images as the plane image . the 3d and 2d mode operations are interchanged with each other in accordance with the condition of the viewer . for instance , when the viewer observing in the 3d mode operation tilts his / her head , a shutter cell which focuses the right image on the right eye and the left image on the left eye is selected . however , these image contains only the horizontal parallax information , so that it is hard to present the image stereoscopic . so , the light source controller 31 changes the mode from 3d to 2d automatically , when the viewer tilts his / her head more than the specific angle which is set up that the fusion of the parallax image is difficult , based on the result sent from the light - cell designator 30 . further , even in the case that the viewer can observe the stereoscopic image in the 3d mode operation ( the state that the parallax images can be fused ) when the viewer wants to observe the plane image in accordance with his / her intention he / she can change the image display mode between the 3d and 2d mode operations at his / her pleasure by sending the signal received in the receiver 29 to the light pass / block controller 31 by the radio such as the remote controller . here , this is not limited to the radio , but other external input system may be adapted . furthermore , according to the present invention , the position , the size of the shutter and the timing of the open / close operation are controlled separately . that is , when several viewers observe it , the shutters associated with their eyes are controlled separately . in the stereoscopic image display apparatus according to the present invention , the same image can be provided in the 3d mode operation to some viewers and in the 2d mode operation to some viewers having some reasons as described above in one display apparatus . further , according to the present invention , the shutter - cells 23 bl , 23 br operated in the 2d mode operation explained in fig2 may be set up as a region 231 including these two shutter - cells . in this case , since it can take wide margin , the viewer can observe the fine normal plane image display even when the viewer moves fast and the movement of the shutter does not catch up . that is , it controls to simultaneously open the left and right shutter - cells , as shown in fig3 c . this is advantageous since it is not needed to often control the shutter - cells when the viewer moves if a wide region like the region 231 is defined in place of the shutter - cells 23 bl , 23 br . further , as shown in fig4 b , when a region 232 operative in the 2d mode operation is defined in covering all the shutter - cells other than those operating in the 3d mode operation , the normal plane image display can be observed by any viewers . that is when a small hatched region , as shown in fig4 b , is defined , only the viewer associated with the shutter - cells 23 al , 23 ar can observe the image in the 3d mode operation , while other viewers can observe the image in the 2d mode operation in any location or posture of the viewers . here , the shutter - cells associated with the eyes of the viewers are explained in the four shutter - cells , that is , shutter - cells addressed to two viewers . however , the number of viewers is not limited . also the number of the shutter - cells is not limited . further , the convex lens 24 , as shown in the fig2 serves to focus the light from the light source onto the eyes of the viewers . then the convex lens 24 may be replaced by any other optical system containing several lenses . for example , as shown in fig5 such an optical system may be comprised of the convex lens 24 , the lcd spatial modulator 25 and a projection lens 56 for projecting lights to the convex fresnel lens 57 in a shape of a light transmission screen . in this case , the image is enlarged to the whole area of the fresnel lens 57 . thus viewers can enjoy a wide screen image . as described above , the optical system is not limited to the single convex lens system . fig6 shows a second preferred embodiment of the present invention . a stereoscopic image display apparatus , as shown in fig6 is characterized by that it is provided with an lcd spatial modulator 66 r for displaying the right image , and the lcd spatial modulator 66 l for displaying the left image . the light from the light source 61 is diffused by diffuser panels 62 r , 62 l , and incidents to the lcd shutter panels 63 r , 63 l . on either lcd shutter panels 63 r , 63 l , the shutter - cells 64 r , 64 l are designated . the designation is carried out by the lcd shutter panel controller 614 . the diffusion light passes through these shutter - cells . here the positions of the shutter - cells 64 r , 64 l are respectively associated with left and right eyes of the viewer 69 in a one - to - one relationship . in the same manner as the above - described first embodiment , the positions of the shutter - cells are controlled by feeding back information of the location of the viewer . that is , an eye - tracker 611 tracks movements of eyes of the viewers based on pictures of the viewers captured by a camera 610 . the shutter - cell designator 613 designates the shutter - cells associated with the eyes of the viewer in reference to the eye - position information . then the lcd shutter panel controller 614 drives the shutter - cells designated by the shutter - cell designator 613 . the light passing through the shutter - cells 64 r , 64 l are condensed by convex lenses 65 r , 65 l , reflected by reflectors 67 r , 67 l , combined by a semi - transparent mirror 68 , then focuses around the eyes of the viewer 69 . between the convex lenses 65 r , 65 l and the viewer 69 , there is located lcd spatial modulators 66 r , 66 l for showing the right eye parallax image and the left eye parallax image under the control of spatial modulator controllers 612 r , 612 l . according to the above configuration a viewer 69 can observe the display image . the operations of the lcd shutter panels 63 r , 63 l in the 3d mode operation for presenting a stereoscopic image to the viewer 69 will be explained in reference to fig6 and 7 . fig7 a shows appearances of the lcd shutter panels 63 r , 63 l in the 3d mode operation . on the lcd shutter panel 63 r the shutter - cells 64 associated with the right eye of the viewer is activated . the light passing through the shutter - cells 64 r is modulated by the lcd spatial modulator 66 r in a state presenting the right image and then focused on the right eye of the viewer 69 . on the lcd shutter panel 63 l the shutter - cells 64 l associated with the left eye of the viewer is activated . the light after passing through the shutter - cells 64 l is modulated by the lcd spatial modulator 66 l in the state presenting the left image and then focused on the left eye of the viewer . according to the operation , the viewer can observe the stereoscopic image . next , the operations of the lcd shutter panel 63 r , 63 l for presenting a normal plane image to the viewer will be explained in reference to fig7 b . fig7 b shows appearances of the lcd shutter panels 63 r , 63 l in the 2d mode operation . on the lcd spatial modulator 63 r the shutter - cells 64 r associated with the right eye of the viewer and the shutter - cells 64 l associated with the left eye of the viewer are activated . the light after passing through the shutter is modulated by the lcd spatial modulator 66 r in the state displaying the right image , and then focused on both the right and left eyes of the viewer . on the lcd 63 l shutter panel , the shutter - cells associated with both eyes of the viewer are deactivated . of if they are activated , the light passing through them fails to reach the eyes of the viewer . according to the above operation , the viewer 69 can receive only the image associated with his / her right eye and thus observes a normal plane image . in the same manner as the embodiment as described above in the 3d and 2d mode operations , even when the viewer observing the image in the 3d mode operation tilts his / her head more than the specific angle which is hard to fuse the parallax image , the lcd shutter panel controller 614 changes the image display mode from the 3d mode operation to the 2d mode operation automatically based on the designation by the shutter - cell designator 613 . even when the viewer can observe the stereoscopic image in the 3d mode operation , i . e ., in the condition that the parallax image is hard to be fused together , the viewer can change the image display mode from the 3d mode operation to the 2d mode operation at his / her pleasure through the interface such as the receiver 615 for receiving the remote control signal from the remote controller operable by the viewer to the shutter - cell designator 613 . here the interface can be realized by any external input system , other than such a remote control system . further , according to the present invention , the shutter - cells 64 r , 64 l operating in the 2d mode operation , as shown in fig7 b , may be replaced by a region 621 including these two shutter - cells , as shown in fig8 a . in this case , it can take a wide margin like the first embodiment . thus the viewer can observe a good quality of the normal plane image display . as shown in fig8 b , by defining a region 622 operating in the 2d mode operation the normal plane image display can be observed by many viewers . here the shutter - cells associated with the eyes of the viewer have been explained as two shutter - cells , that is , the case addressed the single viewer . however , the number of viewers , and the number of shutter - cells are not limited . the convex lens 65 , as shown in fig6 serves to focus the light from the light source on the eyes of the viewers . such a lens system may be replaced with any other optical system containing a plurality of lenses , and thus not limited to the type of one convex lens . here , the image presented in the 2d mode operation has been explained as the right image . however , it may not be limited to the light for the right eye but may be adapted to the left eye . though the right image or the left image is selected by the viewer , in the case that the image signal is recorded at the compression rates different between the right and left images , the image having the lower compression rate will be automatically selected . furthermore , the light source 21 , the diffuse panel 22 , and the lcd shutter panel 23 , as shown in fig2 or the light source 61 , the diffuse panel 62 r and the lcd shutter panel 63 r and the light source 61 , the diffuse panel 62 l and lcd shutter panel 63 l , as shown in fig6 may be replaced with a light source 901 with a two - dimensional configuration including a plurality of light cells . it is also possible to use a monochromic cathode - ray tube 902 , as shown in fig9 b . thus it is not limited by the embodiments as described above . as described above , the present invention can provide a stereoscopic image display capable of presenting both the stereoscopic image display and the normal plane image display or capable of changing between the stereoscopic image display and the normal plane image display in accordance with situations of viewers . so , in the case that the viewer tilts his / her head or the parallax images are hard to be fused together into a stereoscopic image , the viewer can still observe the plane image by changing from the stereoscopic image display . further , even in the case when the viewer is hard to observe the stereoscopic image due to a fatigue in his / her eyes , the normal plane image display is changed from the stereoscopic image display so as to avoid the burden to his / her eyes . as described above , the present invention can provide an extremely preferable stereoscopic image display apparatus . while there have been illustrated and described what are at present considered to be preferred embodiments of the present invention , it will be understood by those skilled in the art that various changes and modifications may be made , and equivalents may be substituted for elements thereof without departing from the true scope of the present invention . in addition , many modifications may be made to adapt a particular situation or material to the teaching of the present invention without departing from the central scope thereof . therefor , it is intended that the present invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the present invention , but that the present invention includes all embodiments falling within the scope of the appended claims . the foregoing description and the drawings are regarded by the applicant as including a variety of individually inventive concepts , some of which may lie partially or wholly outside the scope of some or all of the following claims . the face that the applicant has chosen at the time of filing of the present application to restrict the claimed scope of the protection in accordance with the following claims is not to be taken as a disclaimer or alternative inventive concepts that are included in the contents of the application and could be defined by claims differing in scope from the following claims , which different claims may be adopted subsequently during prosecution , for example , for the purposes of a divisional application .