Abstract:
A binocular display system comprises: a binocular image pickup system that includes a right eye-use image pickup optical system and a left eye-use image pickup optical system; a binocular display system that includes a right eye-use display unit which displays image information picked up by the right eye-use image pickup optical system, and a left eye-use display unit which displays image information picked up by the left eye-use image pickup optical system; and a correlating means that correlates the binocular image pickup system and the binocular image display system. In addition, a binocular display device comprises an image processing unit that processes the image information obtained by the binocular image pickup system. The image processing unit can enlarge an image and display the same on the binocular display system, and correct the movement of the displayed image when at least a prescribed amount of enlargement is carried out.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a binocular display apparatus. 
       BACKGROUND ART 
       [0002]    Various studies have been done on binocular display apparatuses and their applications. For example, their applications as vision aid systems for the visually impaired have been studied. Common causes of vision disorders include eye diseases, such as glaucoma, cataract, night blindness, and age-related macular degeneration, and developmental disorders, such as vision disorders in childhood. As remedies, various aid cameras and aid displays have been proposed. In this context, binocular display apparatuses are employed as aid displays. As one example, there is proposed a goggle-type vision enhancement device in which an image in a region corresponding to a user&#39;s visual field out of a picture taken with a CCD camera is subjected to image processing for viewing by the user through a virtual-image display device (Patent Document 1). For another example, there is proposed a configuration in which image information obtained from an imager is processed to be displayed in a display area on a display such that, on the display, a user can see the processed image in the display area simultaneously with an image of the outside world (Patent Document  2 ). 
       LIST OF CITATIONS 
     Patent Literature 
       [0000]    
       
         Patent Document 1: Japanese Patent Application published as No. 2003-287708 
         Patent Document 2: Japanese Patent No. 4600290 
       
     
       SUMMARY OF THE INVENTION 
     Technical Problem 
       [0005]    However, conventional binocular display apparatuses leave much room for further studies. 
         [0006]    Against the background given above, it is an object of the present invention to propose more useful binocular display apparatuses. 
       Means for Solving the Problem 
       [0007]    According to one aspect of what is disclosed herein, a binocular display apparatus includes: a binocular imaging system including a right-eye imaging optical system and a left-eye imaging optical system; a binocular display system including a right-eye display configured to display image information taken by the right-eye imaging optical system and a left-eye display configured to display image information taken by the left-eye imaging optical system; and correlating means for establishing a correlation between the binocular imaging system and the binocular display system. The correlating means may establish the correlation such that, when a subject taken by the binocular imaging system is displayed by the binocular display system, the convergence angle between right and left eyes seeing the subject displayed by the binocular display system is approximate to the convergence angle observed when the right and left eye really see the subject. The optical axes of the right-eye and left-eye imaging optical systems may be parallel to each other, and the correlating means may establish the correlation such that the optical axis interval between the right-eye and left-eye displays is equivalent to the optical axis interval between the right-eye and left-eye imaging optical systems. 
         [0008]    The binocular display system may be configured to provide a display virtual image at a distance equivalent to the standard subject distance of the binocular imaging system. The binocular display system may have a dioptric power adjusting function. The binocular display system may have at least one of an image enlarging function and an image reducing function. 
         [0009]    The optical axes of the right-eye and left-eye imaging optical systems may be parallel to each other, the optical axis interval of the binocular display system may differ from the optical axis interval of the binocular imaging system, and the correlating means may have an image shifting function based on the difference between the optical axis interval of the binocular imaging system and the optical axis interval of the binocular display system. The binocular display system may have an optical axis interval adjusting function, and the correlating means may have an image shifting function based on optical axis interval adjustment in the binocular display system. The optical axes of the right-eye and left-eye imaging optical systems may be parallel to each other, the binocular display system may have a display optical system different from the imaging optical systems of the binocular imaging system, and the correlating means may have an image shifting function based on the difference between the imaging optical system and the display optical system. 
         [0010]    The optical axis of the binocular imaging system and the optical axis of the binocular display system may coincide with each other. The binocular display apparatus may further include: an image processor configured to process the image information from the binocular imaging system; and a memory configured to store preset information on correction in the image processor. The preset information may be stored separately for the right and left eyes. 
         [0011]    The binocular display apparatus may further include: an image processor configured to be capable of displaying the image information from the binocular imaging system through the binocular display system on an enlarged scale and to correct movement of the displayed image when enlargement higher than a predetermined magnification is performed. The binocular display apparatus may further include: a circumstance sensor configured to detect the circumstances of use; and a controller configured to stop the binocular display system from changing display when the circumstance sensor detects minute vibrations. 
         [0012]    According to another aspect of what is disclosed herein, a binocular display apparatus includes: a binocular imaging system including a right-eye imaging optical system and a left-eye imaging optical system; an image processor configured to process image information obtained by the binocular imaging system; and a binocular display system including a right-eye display and a left-eye display and displaying the image information from the image processor. Here, the image processor is configured to be capable of displaying an image through the binocular display system on an enlarged scale and to correct movement of the displayed image when enlargement higher than a predetermined magnification is performed. The image processor may be configured to correct movement of the displayed image by delaying the movement of the displayed image when enlargement higher than the predetermined magnification is performed. The image processor may be configured to correct movement of the displayed image by reducing the frame rate of image display on the displays when enlargement higher than the predetermined magnification is performed. 
         [0013]    According to yet another aspect of what is disclosed herein, a binocular display apparatus includes: a binocular imaging system including a right-eye imaging optical system and a left-eye imaging optical system; an image processor configured to process image information obtained by the binocular imaging system; a binocular display system including a right-eye display and a left-eye display and displaying the image information from the image processor; a circumstance sensor configured to detect the circumstances of use; and a controller configured to stop the binocular display system from changing display when the circumstance sensor detects minute vibrations. The binocular display apparatus may further include: a processing controller configured to automatically change processing by the image processor based on detection by the circumstance sensor. The processing controller may be configured to effect an automatic return of the processing by the image processor to a standard state based on the detection by the circumstance sensor. 
       Advantageous Effects of the Invention 
       [0014]    It is thus possible to provide more useful binocular display apparatuses as described above. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a block diagram showing the overall configuration of a vision aid system in Example 1 embodying the present invention (Example 1); 
           [0016]      FIG. 2  is a basic flow chart explaining the operation of the central controller in Example 1; 
           [0017]      FIG. 3  is a flow chart showing the details of steps S 22  and S 24  in  FIG. 2 ; 
           [0018]      FIG. 4  is a flow chart showing the details of steps S 26  and S 28  in  FIG. 2 ; 
           [0019]      FIG. 5  is a flow chart showing the details of step S 34  in  FIG. 2 ; 
           [0020]      FIG. 6  is a flow chart showing the details of step S 14  in  FIG. 2 ; 
           [0021]      FIG. 7  is a flow chart showing the details of the abrupt image change alleviating process in a vision aid system in Example 2 embodying the present invention (Example 2); 
           [0022]      FIG. 8  is a block diagram showing the overall configuration of a vision aid system in Example 3 embodying the present invention (Example 3); 
           [0023]      FIG. 9  is a basic flow chart explaining the operation of the central controller in Example 3; 
           [0024]      FIG. 10  is a flow chart showing the details of step S 214  in  FIG. 9 ; 
           [0025]      FIG. 11  is a block diagram showing the overall configuration of a vision aid system in Example 4 embodying the present invention (Example 4); 
           [0026]      FIG. 12A  is a schematic sectional view (a standard state) explaining the principle of dioptric power adjustment in the eyepiece optical systems in Example 4; 
           [0027]      FIG. 12B  is a schematic sectional view (a short-sightedness correcting state) explaining the principle of dioptric power adjustment in the eyepiece optical systems in Example 4; 
           [0028]      FIG. 12C  is a schematic sectional view (a far-sightedness correcting state) explaining the principle of dioptric power adjustment in the eyepiece optical systems in Example 4; 
           [0029]      FIG. 13A  is a schematic diagram (a basic configuration) as to the imaging and displaying of a 3D image in Example 4; 
           [0030]      FIG. 13B  is a schematic diagram (a display state) as to the imaging and displaying of a 3D image in Example 4; 
           [0031]      FIG. 13C  is a schematic diagram (a naked-eye real-view state) as to the imaging and displaying of a 3D image in Example 4; 
           [0032]      FIG. 14A  is a schematic diagram (a display state) as to a near-sighted person in Example 4; 
           [0033]      FIG. 14B  is a schematic diagram (a corrected real-view state) as to a near-sighted person in Example 4; 
           [0034]      FIG. 15A  is a schematic diagram (a display state) as to a far-sighted person in Example 4; 
           [0035]      FIG. 15B  is a schematic diagram (a corrected real-view state) as to a far-sighted person in Example 4; 
           [0036]      FIG. 16A  is a schematic diagram (a basic configuration) as to a close object point in Example 4; 
           [0037]      FIG. 16B  is a schematic diagram (a display state) as to a close object point in Example 4; 
           [0038]      FIG. 16C  is a schematic diagram (a naked-eye real-view state) as to a close object point in Example 4; 
           [0039]      FIG. 17A  is a schematic diagram (a basic configuration) as to a far object point in Example 4; 
           [0040]      FIG. 17B  is a schematic diagram (a display state) as to a far object point in Example 4; 
           [0041]      FIG. 17C  is a schematic diagram (a naked-eye real-view state) as to a far object point in Example 4; 
           [0042]      FIG. 18A  is a schematic diagram (a standard magnification) as to display image enlargement in Example 4; 
           [0043]      FIG. 18B  is a schematic diagram (enlarged) as to display image enlargement in Example 4; 
           [0044]      FIG. 19A  is a schematic diagram (a standard magnification) as to display image reduction in Example 4; 
           [0045]      FIG. 19B  is a schematic diagram (reduced) as to display image reduction in Example 4; 
           [0046]      FIG. 20A  is a schematic sectional view (a basic configuration) of Example 5 embodying the present invention (Example 5); 
           [0047]      FIG. 20B  is a schematic sectional view (with no shifting) of Example 5 embodying the present invention (Example 5); 
           [0048]      FIG. 20C  is a schematic sectional view (with shifting) of Example 5 embodying the present invention (Example 5); 
           [0049]      FIG. 21A  is a schematic sectional view (a basic configuration) of Example 6 embodying the present invention (Example 6); 
           [0050]      FIG. 21B  is a schematic sectional view (with a reduced interpupillary distance) of Example 6 embodying the present invention (Example 6); 
           [0051]      FIG. 21C  is a schematic sectional view (with a increased interpupillary distance) of Example 6 embodying the present invention (Example 6); 
           [0052]      FIG. 22A  is a schematic sectional view (a basic combination) of Example 7 embodying the present invention (Example 7); 
           [0053]      FIG. 22B  is a schematic sectional view (another combination, with no shifting) of Example 7 embodying the present invention (Example 7); and 
           [0054]      FIG. 22C  is a schematic sectional view (another combination, with shifting) of Example 7 embodying the present invention (Example 7). 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     EXAMPLE 1 
       [0055]      FIG. 1  is a block diagram showing the overall configuration of a vision aid system in Example 1 embodying the present invention. The vision aid system of Example 1 includes a goggle-type head mounted display (hereinafter “HMD”)  2  and a controller  4  connected thereto by a cable. The cable includes a parallel data communication line and a power supply line between the HMD  2  and the controller  4 . 
         [0056]    The HMD  2  is worn in further front of ordinary eyeglasses  10  worn in front of a user&#39;s right and left eyes  6  and  8 . Thus, the HMD  2  is used on the assumption that the eyeglasses  10  correct any refraction disorder of the user&#39;s right and left eyes  6  and  8 . To that end, the HMD  2  comprises a body  2   a  and temples  2   b,  and is configured such that, when the temples  2   b  are placed on the ears over the eyeglasses  10 , the body  2   a  is located in front of the lenses of the eyeglasses  10 . 
         [0057]    Inside the body  2   a,  the HMD  2  has a right-eye display  12  and a left-eye display  14 , which each comprise an OLED (organic light-emitting diode) display panel exploiting organic electroluminescence. As will be described later, a driver  16  drives the right-eye and left-eye displays  12  and  14  individually based on a video signal fed from the controller  4  to display right-eye and left-eye images respectively. As indicated by broken-line arrows, virtual images of the displayed images are directed to the right and left eyes  6  and  8  along lines of sight  6   a  and  8   a  by right-eye and left-eye eyepiece optical systems  18  and  20  respectively. Under the control of the controller  4 , the driver  16  also performs focus adjustment on the right-eye and left-eye eyepiece optical systems  18  and  20 , and moreover performs light-of-sight shift adjustment whereby the optical axes of those optical systems are translated to be displaced from the lines of sight  6   a  and  8   a.    
         [0058]    As indicated by a broken-line arrow, a real image of the visual field is imaged on a right-eye image sensor  22  inside the body  2   a  by a right-eye deflecting zoom lens optical system  24 , which deflects light incident along the right-eye line of sight  6   a  by 90 degrees inward (in the diagram, rightward). Likewise, a real image of the visual field is imaged on a left-eye image sensor  26  by a left-eye deflecting zoom lens optical system  28 , which deflects light incident along the left-eye line of sight  8   a  by 90 degrees inward (in the diagram, leftward). As will be described later, the visual-field images taken by the right-eye and left-eye image sensors  22  and  26  are fed via the driver  16  to the controller  4 . The right-eye and left-eye deflecting zoom lens optical systems  24  and  28  have a zooming capability, whereby not only a real-scale (unity) image but also an enlarged image of the actual visual field and a consolidated image of a wide region of the actual visual field can be imaged on the right-eye and left-eye image sensors  22  and  26 . The former is suitable for observation on an enlarged scale, and the latter is suitable to provide within the visual field a visual-field image that is wider than what is actually seen for a user with visual field constriction. 
         [0059]    The imaging optical system employing the right-eye and left-eye deflecting zoom lens optical systems  24  and  28  described above helps reduce thickness in the incident optical axis direction, preventing the body  2   a  from protruding frontward excessively. Moreover, the right-eye and left-eye deflecting zoom lens optical systems  24  and  28  are configured such that the parts of the optical systems after deflection occupy spaces in the directions perpendicular to the lines of sight  6   a  and  8   a  respectively, and that the right-eye and left-eye image sensors  22  and  26  are arranged further inward in the direction of deflection. This arrangement helps avoid arranging components that shield outside the lines of sight  6   a  and  8   a,  so that the actual visual field outside the lines of sight  6   a  and  8   a  can be seen directly. While the human eyes are believed to be able to perceive information within a visual field as wide as about 200 degrees, the information of the visual field displayed on the right-eye and left-eye displays  12  and  14  in Example 1 covers about 40 degrees. Thus, Example 1 is so configured that the visual field outside the information displayed on the right-eye and left-eye displays  12  and  14  can be seen directly to obtain visual information. 
         [0060]    With the configuration described above, in the vision aid system of Example 1, the visual-field images taken by the right-eye and left-eye image sensors  22  and  26  are fed to the controller  4  for processing that suits a user&#39;s symptoms, and the processed images returned from the controller  4  are displayed on the right-eye and left-eye displays  12  and  14  in an observable fashion, so that better visual information is obtained than when the visual field is directly seen with the eyes. For example, a user with night blindness (impaired dark adaptation) can be presented with images processed at an increased gain with dark parts boosted by gamma correction. On the other hand, a user with light aversion (impaired light adaptation) can be presented with images processed with high-luminance parts compressed by gamma correction. For another example, for enhanced legibility of characters and the like, white-black reversed images can be presented. Moreover, the visual field around the image information displayed on the right-eye and left-eye displays  12  and  14  can be seen directly to obtain visual information. Incidentally, as will be described later, the degree of transparency of the directly observed images is controlled to match them with the displayed images. 
         [0061]    As mentioned above, in Example 1 of the present invention, in a normal state, the optical axis of the right-eye eyepiece optical system  18  which directs the virtual image of the right-eye display  12  to the right eye  6  coincides with the incident optical axis of the right-eye deflecting zoom lens optical system  24 . Likewise, the optical axis of the left-eye eyepiece optical system  20  which directs the virtual image of the left-eye display  14  to the left eye  8  coincides with the incident optical axis of the left-eye deflecting zoom lens optical system  28 . As necessary, under the control of the driver  16 , the optical axis of the right-eye or left-eye eyepiece optical system  18  or  20  can be translated to be displaced from the line of sight  6   a  or  8   a.  This makes it possible to cope with, for example, a user with a disorder in the foveal vision due to age-related macular degeneration or the like by shifting the line of sight so that the image taken by the right-eye or left-eye image sensor  22  or  26  can be seen in an unaffected part, that is, elsewhere than in a central part, of the retina. 
         [0062]    Moreover, as described above, Example 1 of the present invention is so configured that the actual visual field outside the lines of sight  6   a  and  8   a  can be seen directly as the background. Moreover, in the optical path, indicated by an arrow  30 , leading into the right eye from outward, a right-eye variable-transmittance ND filter  32  is provided. The right-eye variable-transmittance ND filter  32  comprises, for example, a liquid crystal shutter, and its transmittance is variable, under the control of the driver  16 , between a maximum transmittance and a light intercepting state. Likewise, in the optical path, indicated by an arrow  34 , leading into the left eye from outward, a left-eye variable-transmittance ND filter  36  is provided, and its transmittance is variable, under the control of the driver  16 , between a maximum transmittance and a light intercepting state. Thus, the transmittances of the right-eye and left-eye variable-transmittance ND filters  32  and  36  can be changed independently of each other. Changing their transmittances serves not only to assist the pupil&#39;s ability to adapt to change of lightness in the ambience, but also to enhance the visibility of the display (the right-eye and left-eye displays  12  and  14 ) by changing transmittances according to change of lightness, and in addition to match the image on the display with the directly observed image as the background. Furthermore, when white-black reversed display is performed on the display, the right-eye and left-eye variable-transmittance ND filters  32  and  36  are brought into the light intercepting state so as not to interfere observation of a white-black reversed image. 
         [0063]    As will be clear from  FIG. 1 , the above-described components of Example 1 are all housed inside the body  2   a,  and no part of the body  2   a  protrudes from the front face. Accordingly, when seen from a person facing the user wearing the HMD  2 , the HMD  2  appears something like ordinary sunglasses, and this alleviates the sense of annoyance of being observed with a special device. 
         [0064]    The driver  16  in the body  2   a  of the HMD  2  is connected to the controller  4  by parallel data communication and a power supply line  38  to allow mutual communication and supply of electric power from the controller  4  to the HMD  2 . Moreover, to allow change of the image processing performed for the right-eye and left-eye displays  12  and  14 , an ambient light sensor  40  is provided in the temples  2   b  of the HMD  2 , and information on the ambient light is fed to the controller  4  across a communication line  42 . Furthermore, to alleviate abrupt image change as occurs when the user changes the direction of the face, in particular with an enlarged image, an acceleration sensor  44  is provided in the temples  2   b,  and information on the movement and the like of the face is fed to the controller  4  across a communication line  46 . The parallel communication, the power supply line  38 , and the communication lines  42  and  46  are in practice integrated into a single connection cable. Although  FIG. 1  shows a configuration where the ambient light sensor  40  and the acceleration sensor  44  communicate directly with the controller, a configuration is also possible where communication is conducted via the driver  16  across parallel data communication and the power supply line  38 . 
         [0065]    The controller  4  has an interface  48  for communication with the HMD  2  and for supply of electric power to the HMD  2  as described above. An image processor  50  in the controller  4  processes images received via the driver  16  across parallel data communication and the power supply line  38  from the right-eye and left-eye image sensors  22  and  26  of the HMD  2 , and feeds the result, as image data suitable to assist the user, to a display controller  52 . From the display controller  52 , the image data is transmitted across the parallel data communication and the power supply line  38  so that, based on the received image data, the driver  16  drives the right-eye and left-eye displays  12  and  14  to display images. Moreover, a background controller  54  controls the right-eye and left-eye variable-transmittance ND filters  32  and  36  across the parallel data communication and the power supply line  38 . 
         [0066]    A preset memory  56  stores preset values for image processing information and transmittance information (information on the transmittances of the right-eye and left-eye variable-transmittance ND filters  32  and  36 ) that suit the user&#39;s specific symptoms and the ambient light. An operation panel  58 , in coordination with display on a controller display  60 , accepts operations for entering preset values as mentioned above and operations for selecting image processing such as white-black reversal. A central controller  62  controls the image processor  50  according to the image processing information in the preset memory  56  as well as operations on the operation panel  58  and information from the ambient light sensor  40  and the acceleration sensor  44 . The central controller  62  also controls a background controller  54  according to the transmittance information in the preset memory  56  as well as information from the ambient light sensor  40 . Control data for the background controller  54  is transmitted across parallel data communication and the power supply line  38 , and based on the received data, the driver  16  varies the transmittances of the right-eye and left-eye variable-transmittance ND filters  32  and  36  to control the lightness of the directly observed background. The central controller  62  further controls the display controller  52  and the controller display  60  in connection with the functions mentioned above. A power supply  64  supplies electric power to the entire controller  4  and also, via the interface  48 , to the HMD  2 . 
         [0067]      FIG. 2  is a basic flow chart explaining the operation of the central controller  62  in Example 1. The flow starts when electric power starts to be supplied to the system. At Step S 2 , whether or not any preset value is stored is checked. If any, the flow proceeds to step S 4 , where the preset values is read from the preset memory  56 , and the flow then proceeds to step S 6 . On the other hand, if, at step S 2 , no preset value is stored, the flow proceeds to step S 8 , where default values specifying no correction in image processing are read, and the flow then proceeds to step S 6 . 
         [0068]    At step S 6 , imaging by the right-eye and left-eye image sensors  22  and  26  is started. The flow then proceeds to step S 10 , where display starts to be controlled in a standard state with predetermined lightness as a reference, and also the transmittances of the right-eye and left-eye variable-transmittance ND filters  32  and  36  start to be controlled to produce a background in a standard state that matches the display. 
         [0069]    Subsequently, at step S 12 , whether or not an operation to set a preset value has been done is checked. If a setting operation is recognized to have been done, the flow proceeds to step S 14 , where a preset value setting process is performed, and the flow then proceeds to step S 16 . On the other hand, if, at step S 12 , no operation to set a preset value is recognized, the flow proceeds directly to step S 16 . The preset value setting process at step S 14  will be described in detail later. 
         [0070]    At step S 16 , whether or not a preset value indicating that the user has a disorder in the foveal vision is stored is checked, and if so, the flow proceeds to step S 18 , where a light-of-sight shifting process is performed, and the flow then proceeds to step S 20 . On the other hand, if, at step S 16 , the user is recognized not to have a disorder in the foveal vision, the flow proceeds directly to step S 20 . This establishes a normal state where, as described above, the optical axes of the right-eye and left-eye eyepiece optical systems  18  and  20  coincide with the incident optical axes of the right-eye and left-eye deflecting zoom lens optical systems  24  and  26  respectively. 
         [0071]    At step S 20 , whether or not there has been a change in the lightness of the ambient light is checked, and if so, a right-eye display changing process at step S 22  and a left-eye display changing process at step S 24  are performed successively, and the flow proceeds to step S 26 . In this way, the right-eye and left-eye display changing processes are performed independently of each other. At step S 26 , a right-eye background changing process is performed, and subsequently, at step S 28 , a left-eye background changing process is performed. The flow then proceeds to step S 30 . In this way, the right-eye and left-eye background changing processes too are performed independently of each other. On the other hand, if, at step S 20 , there has been no change in the lightness of the ambient light, the flow proceeds directly to step S 30 . 
         [0072]    At step S 30 , whether or not an operation for white-black reversal has been done is checked, and if so, the flow proceeds to step S 32 , where white-black reversed display is performed while the background is brought into a light-intercepting state so as not to interfere with the observation of the white-black reversed display, and the flow then proceeds to step S 34 . On the other hand, if, at step S 30 , no operation for white-black reversal is recognized, the flow proceeds directly to step S 34 . At step S 34 , an abrupt image change alleviating process (described in detail later) is performed. Then, at step S 36 , whether or not electric power is being supplied is checked and, if so, the flow returns to step S 12  so that thereafter, so long as electric power is recognized to be being supplied, steps S 12  through S 36  are repeated. On the other hand, if, at step S 36 , electric power is not recognized to be being supplied, the flow ends immediately. 
         [0073]      FIG. 3  is a flow chart showing the details of the right-eye display changing process at step S 22  and the left-eye display changing process at step S 24 . What is done is common to those two steps, but is performed separately for the right and left eyes as shown in  FIG. 2 . At the start, the flow proceeds to step S 42 , where it is checked whether or not the change in the ambient light detected at step S 20  in  FIG. 2  is equal to or larger than a predetermined value set beforehand for the display changing process. If the change is equal to or smaller than the predetermined value and does not require the display changing process, the flow ends immediately, and a jump is made back to step S 26  in  FIG. 2 . 
         [0074]    On the other hand, if, at step S 42 , a change larger than the predetermined value is detected, the flow proceeds to step S 44 , where whether or not the change has caused the ambient light to be higher than a predetermined value is checked. If, at step S 44 , the ambient light is detected having become higher than the predetermined value, then at step S 46 , the gain of the image sensors  22  and  26  is reduced, and the flow proceeds to step S 48 . At step S 48 , whether or not the user has impaired light adaptation is checked, and if so, the flow proceeds to step S 50 , where gamma correction is performed to compress high-luminance parts, and the flow then proceeds to step S 52 . At step S 52 , edge enhancement is further performed, and the flow proceeds to step S 54 . On the other hand, if, at step S 44 , the ambient light is not detected having become higher than the predetermined value, or if, at step S 48 , the user is not confirmed to have impaired light adaptation, the flow proceeds directly to step S 54 . 
         [0075]    At step S 54 , whether or not the change has caused the ambient light to be lower than the predetermined value is checked. If the ambient light is detected having become lower than the predetermined value, then at step S 56 , the gain of the image sensors  22  and  26  is increased, and the flow proceeds to step S 58 . At step S 58 , whether or not the user has impaired dark adaptation is checked, and if so, the flow proceeds to step S 60 , where gamma correction is performed to boost low-luminance parts, and the flow then proceeds to step S 62 . At step S 62 , contrast enhancement is further performed, and the flow proceeds to step S 64 . On the other hand, if, at step S 54 , the ambient light is not detected having become lower than the predetermined value, or if, at step S 58 , the user is not confirmed to have impaired dark adaptation, the flow proceeds directly to step S 64 . 
         [0076]    At step S 64 , a counter for performing display change correction according to the time required by the pupil to adapt to a change in lightness is reset and started, and the flow proceeds to step S 66 . At step S 66 , it is checked whether or not pupil reaction correction based on the previous change in lightness is underway, and if so, the flow proceeds to step S 68 , where the previous pupil reaction correction is canceled, and the flow then proceeds to step S 70 . On the other hand, if, at step S 66 , no previous pupil reaction correction is detected being underway, the flow proceeds directly to step S 70 . At step S 70 , pupil reaction correction is started and in addition a process for automatically ending the pupil reaction correction at the end of a pupil reaction based on the counter is started, and the flow then ends. 
         [0077]      FIG. 4  is a flow chart showing the details of the right-eye and left-eye background changing processes at steps S 26  and S 28  in  FIG. 2 . What is done is common to those two steps, but is performed separately for the right and left eyes as shown in  FIG. 2 . At the start, the flow proceeds to step S 82 , where it is checked whether or not the change in the ambient light detected at step S 20  in  FIG. 1  has caused the ambient light to be higher than a predetermined value. Typically, the predetermined value at step S 82  in  FIG. 4  has a lower level than the predetermined value at step S 44  in  FIG. 3 . 
         [0078]    If, at step S 82 , the ambient light is detected having become higher than the predetermined value, the flow proceeds to step S 84 , where the transmittances of the right-eye and left-eye variable-transmittance ND filters  32  and  36  are reduced according to the increase in the ambient light, and the flow proceeds to step S 86 . At step S 86 , it is checked whether or not a display changing process has been performed based on the latest change in the ambient light, and if so, the flow proceeds to step S 88 , where the transmittances of the right-eye and left-eye variable-transmittance ND filters  32  and  36  are changed according to the display change, and the flow then proceeds to step S 90 . If, at step S 82 , the ambient light is not detected having become higher than the predetermined value, or if, at step S 86 , no display changing process is detected having been performed, the flow proceeds directly to step S 90 . 
         [0079]    At step S 90 , it is checked whether or not the change in the ambient light detected at step S 20  in  FIG. 1  has caused the ambient light to be lower than a predetermined value. Typically, the predetermined value at step S 90  in  FIG. 4  has a higher level than the predetermined value at step S 54  in  FIG. 3 . If, at step S 90 , the ambient light is detected having become lower than the predetermined value, the flow proceeds to step S 92 , where whether or not the transmittances of the right-eye and left-eye variable-transmittance ND filters  32  and  36  are already at their maximum. If not, the flow proceeds to S 94 , where the transmittances of the right-eye and left-eye variable-transmittance ND filters  32  and  36  are increased according to the increase in the ambient light, and the flow then proceeds to step S 96 . The increase here, however, does not exceed the maximum transmittance. On the other hand, if, at step S 92 , the transmittances of the right-eye and left-eye variable-transmittance ND filters  32  and  36  are already at their maximum, the flow proceeds directly to step S 96 . 
         [0080]    At step S 96 , it is checked whether or not a display changing process has been performed based on the latest change in the ambient light, and if so, the flow proceeds to step S 98 , where the transmittances of the right-eye and left-eye variable-transmittance ND filters  32  and  36  are changed according to the display change, and the flow then proceeds to step S 100 . The increase here, however, does not exceed the maximum transmittance. On the other hand if, at step S 90 , the ambient light is not detected having become lower than the predetermined value, or if, at step S 96 , no display changing process is detected having been performed, the flow proceeds directly to step S 100 . 
         [0081]    At step S 100 , it is checked whether or not any pupil reaction correction process that was started for display change in  FIG. 3  is underway, and if so, the flow proceeds to step S 102 , where corresponding correction of the transmittances of the right-eye and left-eye variable-transmittance ND filters  32  and  36  is started and in addition a process for automatically ending the correction according to the pupil reaction correction for display change is started, and the flow then ends. 
         [0082]      FIG. 5  is a flow chart showing the details of the abrupt image change alleviating process at step S 34  in  FIG. 2 . When the flow starts, at step S 112 , whether or not the display magnification is real-scale (unity) or higher is checked. If not, that is, if the display magnification is equal to or lower than the magnification of the background and thus no alleviation of abrupt image change is needed even when, for example, the direction of the face is changed, the flow ends immediately, and a jump is made to step S 36  in  FIG. 2 . 
         [0083]    By contrast, if, at step S 112 , the display magnification is detected being real-scale or higher, the flow proceeds to step S 114 , where it is checked whether or not acceleration resulting from the direction of the face being changed is detected. If acceleration is detected, the flow proceeds to step S 116 , where the display of the previous frame on the right-eye and left-eye displays  12  and  14  is maintained, and the flow proceeds to step S 118 . At step S 118 , it is checked whether or not a time set beforehand according to the display magnification (for example, a time corresponding to three frames for a display magnification of  2  times) has elapsed. If not, the flow returns to step S 116 , and thereafter, until the time is detected to have elapsed, steps S 116  and S 118  are repeated to maintain the previous frame. On the other hand, if, at step S 118 , the time is detected to have elapsed, the flow proceeds to step S 120 . 
         [0084]    At step S 120 , the check for acceleration is done once again so that, if no acceleration is detected any longer as a result of the face ceasing to move, the flow proceeds to step S 122 , where the frame next to the one maintained at step S 116  is displayed, and the flow then proceeds to step S 126 . The display of the next frame at step S 112  is performed at a higher frame rate than normally is. At step S 126 , it is checked whether or not the display has caught up with the current frame. If not, the flow returns to step S 120 . Thereafter, unless acceleration is detected anew at step S 120  and in addition the current frame is caught up with at step S 126 , steps S 120  through S 126  are repeated, so that a return to the current frame is made at a frame rate higher than the normal frame rate. When, at step S 126 , the current frame is detected being displayed, the flow ends. In this way, abrupt image change occurring when the direction of the face is changed at a high magnification is alleviated, and the motion of the image is delayed. This delay is canceled quickly when the face ceases to move. On the other hand, if, at step S 120 , acceleration is detected and the face keeps moving, the flow proceeds to step S 124 , where the current frame is displayed, and the flow then ends. In this way, while the face keeps moving, abrupt image change is alleviated through sporadic skipping of frames. 
         [0085]      FIG. 6  is a flow chart showing the details of the preset value setting process at step S 14  in  FIG. 2 . When the flow starts, at step S 132 , whether or not the setter is a medical doctor is checked. If so, the flow proceeds to step S 134 , where a doctor setting process is performed, and the flow then proceeds to step S 136 . On the other hand, if, at step S 132 , the setter is not recognized to be a doctor, the flow proceeds directly to step S 136 . At step S 136 , whether or not the setter is an orthoptist is checked. If so, the flow proceeds to step S 138 , where an orthoptist setting processing is performed, and the flow then proceeds to step S 149 . On the other hand, if, at step S 136 , the setter is not recognized to be an orthoptist, the flow proceeds directly to step S 140 . 
         [0086]    At step S 140 , whether or not the setter is the user himself is checked. If so, at step S 142 , right-eye setting is started and, at step S 144 , initial ambient light setting is performed. During setting by a user, the user himself actually wears the HMD  2  and sees the right-eye display  12  to check whether or not a setting is proper. Specifically, at step S 146 , a display correction parameter is changed by the user himself. Then, at step  5148 , the user is prompted to judge whether or not the image observed on the right-eye display  12  is optimal. If the user does not find it optimal, the flow returns to step S 146 , and thereafter steps S 146  and S 148  are repeated to permit the user to change the parameter and judge the result repeatedly. Then if, at step S 148 , the user finds what he observes optimal and operates the operation panel  58  accordingly, the flow proceeds to step S 150 , where the parameter in that state is stored. The flow then proceeds to step S 152 . 
         [0087]    At step S 152 , it is checked whether or not cumulative storage of parameters, which are stored as described above, has been performed a predetermined number of times. If, at step S 152 , cumulative storage has not been performed the predetermined number of times yet, the flow returns to step S 146 , where steps S 146  through S 152  are repeated until cumulative storage is performed the predetermined number of times. On the other hand, if, at step S 152 , cumulative storage has been performed the predetermined number of times, the flow proceeds to step S 154 , where the stored parameters are averaged and setting parameters are determined definitively. 
         [0088]    Subsequently, at step S 156 , the ambient light is changed automatically for the purpose of setting, and the flow then proceeds to step S 158 . At step S 158 , whether or not the ambient light changing process has been completed is checked. If the changing process has not been completed, the flow returns to step S 146 , and thereafter, so long as ambient light changing is not completed, steps S 146  through S 158  are repeated, so that right eye setting is continued. On the other hand, if, at step S 158 , the ambient light changing process is completed, the flow proceeds to a left-eye setting process at step S 160 . The details of the left-eye setting process at step S 160  are the same as those of the right-eye setting process, and for simplicity&#39;s sake, the whole process is illustrated in an integrated fashion at step S 160 . When the left-eye setting process at step S 160  is completed, the flow ends, and a jump is made back to step S 16  in  FIG. 2 . On the other hand, if, at step S 140 , the setter is not detected being the user himself, the flow ends immediately. 
         [0089]    The various features of Example 1 described above can be implemented not only in Example 1 described above but also, so long as they provide their benefits, in any other examples. For example, although the flow in  FIG. 3  deals with a configuration where, for a user with impaired light adaptation, edge enhancement is performed and, for a user with impaired dark adaptation, contrast enhancement is performed, what process to perform in what case is arbitrary: edge enhancement and contrast enhancement may both be adopted irrespective of whether the user has impaired light adaptation or impaired dark adaptation. 
       Example 2 
       [0090]      FIG. 7  is a flow chart showing the details of the abrupt image change alleviating process in a vision aid system in Example 2 embodying the present invention. Example 2 shares the same overall configuration as that of Example 1 shown in the block diagram in  FIG. 1 , and shares the same basic operation as that of Example 1 shown in the basic flow chart in  FIG. 2 . Accordingly, for common features, Example 1 is to be referred to auxiliarily, and no overlapping description will be repeated. Example 2 differs from Example 1 in the specific configuration of the abrupt image change alleviating process at step S 34  in  FIG. 2 . The flow chart in  FIG. 7  thus shows the details of step S 34  in  FIG. 2 , which is referred to auxiliarily in connection with Example 2. 
         [0091]    When the flow in  FIG. 7  starts, at step S 162 , whether or not acceleration equal to or more than a predetermined quantity is detected is checked. If such acceleration is detected, the flow proceeds to step S 164 , where it is checked whether or not a predetermined time (for example, two seconds) has elapsed since acceleration was detected for the first time in a sequence of acceleration detection events. If the predetermined time has not elapsed, the flow proceeds to step S 166 , where a historical analysis of the sequence of acceleration detection events is performed, and the flow then proceeds to step S 168 . At step S 168 , it is checked whether or not a predetermined time (for example, 0.5 seconds) has elapsed since the analysis was started. If the predetermined time has not elapsed, the flow returns to step S 166 , and thereafter, until the predetermined time elapses, steps S 166  and S 168  are repeated to continue the analysis. 
         [0092]    On the other hand, if, at step S 168 , the predetermined time is recognized to have elapsed since the analysis was started, the flow proceeds to step S 170 , where it is checked whether or not the result of the historical analysis indicates that the detected sequence of changes in acceleration corresponds to minute vibrations. If minute vibrations are detected, the flow proceeds to step S 172 , where the display of the previous frame is maintained and the display is kept from being changed. This is to prevent image shake resulting from minute vibrations such as involuntary quivering of the body. Then, at step S 174 , whether or not acceleration in the same direction is detected is checked. 
         [0093]    If, at step S 174 , no acceleration in the same direction is detected, the flow returns to step S 164 , and thereafter, so long as it is not recognized at step S 164  that the predetermined time has elapsed since acceleration was detected for the first time, steps S 164  through S 174  are repeated. On the other hand, if, at step S 174 , acceleration in the same direction is detected, it is judged that the user made an intentional motion, as by changing the direction of the face, and the flow proceeds to step S 176 . At step S 176 , the display is changed from the change-inhibited state to the current frame, and the flow proceeds to step S 178 . Incidentally, if, at step S 170 , the historical analysis does not indicate minute vibrations, the flow proceeds to step S 178  immediately. 
         [0094]    At step S 178 , the current display magnification is checked, and the flow then proceeds to step S 180 , where whether or not the display magnification is real-scale (unity) or higher is checked. If it is real-scale or higher, then, at step S 182 , magnification-dependent frame skipping is specified, and the flow proceeds to step S 184 . In the magnification-dependent frame skipping at step S 182 , frame skipping that depends on the magnification is performed, as by reducing the frame rate to one-half when the magnification is 1.5 times and reducing the frame rate to one-third when the magnification is 2 times, so that, the higher the magnification, the lower the frame rate. This prevents subtle movements of the image in a short period, and thereby prevents motion sickness or the like due to an enlarged image. On the other hand, if, at step S 180 , the image is not real-scale or higher, the flow proceeds to step S 186 , where display at the normal frame rate is specified, and the flow proceeds to step S 184 . 
         [0095]    At step S 184 , whether or not there is acceleration is detected once again, and if acceleration is still detected, the flow returns to step S 164  so that thereafter, so long as it is not recognized at step S 164  that the predetermined time has elapsed since acceleration was detected for the first time, steps S 164  through S 188  are repeated. On the other hand, if, at step S 184 , it is confirmed that no acceleration is detected, the flow proceeds to step S 188 , where display of the current frame is specified and the flow ends. 
         [0096]    If, at step S 164 , it is detected that the predetermined time has elapsed since acceleration was detected for the first time, even if acceleration is still detected, the flow ends immediately. This is to prevent the other tasks in  FIG. 2  from being kept unexecuted as a result of the flow in  FIG. 7  being continued for a long time. As will be clear from  FIG. 2 , unless there is another task, the step S 34  is reached in the course of repetition of steps S 12  through S 36 ; thus, the flow in  FIG. 7  is repeated, and whenever acceleration is detected, the corresponding function in  FIG. 7  can be continued. Incidentally, if, at step S 162 , no acceleration is detected, the flow proceeds to step S 190 , where display at the normal frame rate is specified and the flow ends. In this case, substantially none of the operations in the flow in  FIG. 7  are performed; even so, step S 190  is provided to cope with a case where step S 162  is reached in other than a normal display state and no acceleration is detected. 
       Example 3 
       [0097]      FIG. 8  is a block diagram showing the overall configuration of a vision aid system in Example 3 embodying the present invention. The configuration of Example 3 in  FIG. 8  has much in common with Example 1 in  FIG. 1 ; accordingly the same parts are identified by the same reference signs, and no overlapping description will be repeated. A first difference of Example 3 from Example 1 is that a pulse sensor  66  for detecting the pulse is provided in the temples  2   b  so that information as to whether the user is at rest or in action, as in the course of walking, is fed to the controller  4  across a communication line  68 . As in Example 1, parallel data communication, the power supply line  38 , and the communication lines  42 ,  46 , and  68  are in practice integrated into a single connection cable. Again, although  FIG. 8  shows a configuration where the ambient light sensor  40 , the acceleration sensor  44 , and the pulse sensor  66  communicate directly with the controller  4 , a configuration is also possible where communication is conducted via the driver  16  across parallel data communication and the power supply line  38 . 
         [0098]    A second difference of the Example 3 shown in  FIG. 8  from Example 1 in  FIG. 1  is that a line-of-sight sensor  70  is provided in the HMD  2  to detect the movement of the user&#39;s line of sight. Information on the movement of the user&#39;s line of sight and the like as detected by the line-of-sight sensor  70  is fed to the controller  4  via the driver  16  by parallel data communication. The pulse sensor  66  and the line-of-sight sensor  70  will be described in detail later. In Example 3, the ambient light sensor  40 , the acceleration sensor  44 , the pulse sensor  66 , the line-of-sight sensor  70 , and the like serve to detect the circumstances in which the HMD  2  is used, and are thus collectively referred to as circumstance sensors. 
         [0099]    A third difference of Example 3 shown in  FIG. 8  from Example 1 in  FIG. 1  is that the controller  4  has a mode memory  72  in which different modes, such as an enlargement mode, a wide mode, and a white-black reversal mode, are registered in association with learned information. Learned information is registered for each mode through the learning, in that mode, of what the different circumstance sensors detect and how the operation panel  58  is operated. Based on the information registered in the mode memory  72 , and in coordination with a central controller  74 , restrictions are imposed on the selection of modes on the operation panel  58 , and registered modes are selected automatically. The details will be given later. 
         [0100]      FIG. 9  is a basic flow chart explaining the operation of the central controller  74  in Example 3. The flow in  FIG. 9  has much in common with the flow in  FIG. 2  in Example 1; accordingly, common steps are identified by common step numbers, and no overlapping description will be repeated; likewise, common groups of steps are illustrated in an integrated fashion, and no overlapping description will be repeated. Specifically, the start-up process at step S 192  has steps S 2 , S 4  and S 8  in  FIG. 2  integrated together; the presetting/line-of-sight shifting process at step S 194  has steps S 12  through S 18  in  FIG. 2  integrated together; and the display/background changing process at step S 196  has steps S 22  through S 28  in  FIG. 2  integrated together. 
         [0101]    When step S 198  is reached through the display/background changing process at step S 196 , it is checked whether or not a manual mode registration operation has been done to selectably register a mode other than a normal mode, such as an enlargement mode, a wide mode, or a white-black reversal mode. If a mode registration operation has been done, the flow proceeds to step S 200 , where a manual mode registration process according to the operation is performed, and the flow then proceeds to step S 202 . On the other hand, if, at step S 198 , no mode registration operation is detected, the flow proceeds directly to step S 202 . 
         [0102]    At step S 202 , whether or not a manual operation to select a mode has been done is checked. If a mode selection operation has been done, the flow proceeds to step S 204  and the following steps to detect the circumstances in which the operation was done. Specifically, at step S 204 , the ambient light is detected with the ambient light sensor  40 ; then at step S 206 , acceleration is detected with the acceleration sensor  44 ; and then at step S 208 , the pulse is detected with the pulse sensor  66 . Moreover, at step S 210 , the movement of the line of sight is detected with the line-of-sight sensor  70 . 
         [0103]    Subsequently, at step S 212 , an automatic learning registration process is performed whereby what the different circumstance sensors detected when the mode was selected manually is learned and is automatically registered in that mode. In this process, for example, if an enlargement mode and a white-black reversal mode were selected in a still state free of acceleration and in addition in a resting state based on the pulse with only a limited movement of the line of sight detected, then it is learned that the enlargement mode and the white-black reversal mode are to be selected in such states, and those detected states are registered in the enlargement mode and the white-black reversal mode. That is, a registration is made on the assumption that, in such states, the user is interpreted to have selected the enlargement mode and the white-black reversal mode to read a book or viewing a document. 
         [0104]    The information registered through the automatic mode learning process at step S 212  is used in the cross-checking of properness of automatic selection of a general mode as will be described later, and also in automatic custom mode setting based on fulfilment of a learning result condition unique to a user. On completion of the automatic mode learning process at step S 121 , the flow proceeds to step S 214 . On the other hand, if, at step S 202 , no mode selection operation is detected, the flow proceeds directly to step S 214 . At step S 214 , a mode changing process is performed, which will be described in detail later. On completion of the mode changing process at step S 214 , the flow proceeds to step S 34 . Step S 34  and the following steps are shared with  FIG. 2 . 
         [0105]      FIG. 10  is a flow chart showing the details of the mode changing process at step S 214  in  FIG. 9 . When the flow starts, at step S 222 , it is checked whether or not a manual operation to switch to a wide mode has been done. If no such operation is detected, the flow proceeds to step S 224 , where it is checked whether or not a manual operation to switch to an enlargement mode has been done. If a manual operation to switch to an enlargement mode is detected, the flow proceeds to step S 226 , where it is checked whether or not acceleration indicating that the user is moving is detected. If no acceleration is detected, the flow proceeds to step S 228 , where the magnification is changed as operated (in this case, to a magnification for the “enlargement mode”), and the flow then proceeds to step S 230 . 
         [0106]    On the other hand, if, at step S 226 , acceleration indicating that the user is moving is detected, the flow proceeds to step S 232 , where an indication to the effect that enlargement is inhibited is displayed on the controller display  60 , and the flow proceeds to step S 230  without changing the magnification. The message to the effect that enlargement is not permitted may be displayed in a form superimposed on either of the images of the right-eye and left-eye image sensors  22  and  26 . 
         [0107]    On the other hand, if, at step S 222 , a manual operation to switch to a wide mode is detected having been done, the flow proceeds directly to step S 228 , where the magnification is changed as operated (in this case, to a magnification for the “wide mode”), and the flow proceeds to step S 230 . In this way, an operation to reduce the magnification does not pose a great danger even to a user who is moving, and accordingly the operation is performed immediately without checking for acceleration. Incidentally, if, at step S 224 , no enlargement mode operation is detected, this means that no manual operation to change the magnification has been done, and thus the flow proceeds to step S 23  immediately. 
         [0108]    At step S 230 , whether or not the user has visual field constriction is checked. If the user does not have visual field constriction, the flow proceeds to step S 234 , where real-scale display is set as a standard mode, and the flow then proceeds to step S 236 . On the other hand, if, at step S 230 , the user is recognized to have visual field constriction, the flow proceeds to step S 238 , where wide display is set as a standard mode, and the flow proceeds to step S 236 . 
         [0109]    Step S 236  and the following steps relate to automatic mode change. First, at step S 236 , based on the acceleration sensor  44 , whether or not the user is in a still state is checked. If the user is in a still state, the flow proceeds to step S 240 , where, based on the pulse sensor  66 , whether or not the user in in a resting state is checked. If the user is in the resting state, the flow proceeds to step S 242 , where it is checked whether or not automatically switching to the enlargement mode in such states contradicts the user&#39;s manual setting behavior thus far. If no contradiction is recognized, then, at step S 244 , the enlargement mode is automatically set, and the flow proceeds to step S 246 . On the other hand, if, at step S 236 , no still state is detected, or if, at step S 240 , no resting state is detected, or if, at step S 242 , contradiction with learned information is detected, the flow proceeds to step S 246  without automatically setting the enlargement mode. Here, contradiction with learned information is recognized in such cases as where, despite a still state and in addition a resting state being detected in the automatic registration process from step S 202  through S 212  in  FIG. 9 , there is scarce history of the enlargement mode having been selected manually, or where there is a history of the enlargement mode, once automatically set based on a still state and in addition a resting state, having been cancelled manually. In such cases, even if a still state and a resting state are detected, it is highly likely that automatically setting the enlargement mode will be contrary to the user&#39;s intention, and therefore the flow proceeds to step S 246  without automatically setting the enlargement mode. 
         [0110]    At step S 246 , the movement of the user&#39;s line of sight based on the output of the line-of-sight sensor  70  is compared with reference data indicating reading-pattern line-of-sight movement, and it is checked whether or not the movement of the user&#39;s line of sight corresponds to the reading-pattern line-of-sight movement. If it is recognized as the reading-pattern line-of-sight movement, the flow proceeds to step S 248 , where it is checked whether or not automatically switching to the white-black reversal mode when reading-pattern movement is detected does not contradict the user&#39;s manual setting behavior thus far. If no contradiction is recognized, then, at step S 250 , the white-black reversal mode is automatically set, and the flow proceeds to step S 252 . On the other hand, if, at step S 246 , no reading-pattern line-of-sight movement is detected, or if, at step S 248 , contradiction with learned information is detected, the flow proceeds to step S 252  without automatically setting the white-black reversal mode. Here, contradiction with learned information is recognized, as described above in connection with step S 242 , in cases such as where, despite reading-pattern line-of-sight movement being detected in the automatic registration process from step S 202  through S 212  in  FIG. 9 , there is scarce history of the white-black reversal mode having been selected manually, or where there is a history of the white-black reversal mode, once automatically set based on reading-pattern line-of-sight movement, having been cancelled manually. In such cases, even if reading-pattern line-of-sight movement is detected, it is highly likely that automatically switching to the white-black reversal mode will be contrary to the user&#39;s intention, and accordingly the flow proceeds to step S 252  without automatically switching to the white-black reversal mode. 
         [0111]    In the automatic setting from step S 236  through S 250 , if the automatic setting of the enlargement mode at step S 244  is gone through and then the automatic setting of the white-black reversal mode at step S 250  is performed, enlarged display is white-black reversed. On the other hand, if the automatic setting of the enlargement mode at step S 244  is performed but no reading-pattern line-of-sight movement is detected at step S 246 , the user may be, for example, sitting on a stool and performing assembly work or the like, and thus white-black reversal, which is suitable for the reading of characters, is often unsuitable. Accordingly, only the automatic setting of the enlargement mode is performed before step S 252  is reached. 
         [0112]    The automatic setting from step S 236  through S 250  relates to automatic setting of comparatively general modes such as an enlargement mode and a white-black reversal mode. By contrast, steps S 252  through S 254  are provided to select and automatically set, according to the circumstances, one of a plurality of modes (including at least specific modes under specific conditions and a standard mode set specifically for the user) that are custom-set for a particular user to suit his symptoms such as impaired light or dark adaptation and an abnormal visual field. Specifically, at step S 252 , whether a condition is one that was custom-set is checked, and if so, an automatic custom mode setting process at step S 254  is initiated, where a mode setting is automatically changed, and the flow then proceeds to step S 256 . On the other hand, if, at step S 252 , a condition is not detected being a custom-set one, the flow proceeds directly to step S 256 , where the currently set mode is maintained. 
         [0113]    At step S 256 , whether or not movement acceleration has been detected is checked. If movement acceleration has been detected, the flow proceeds to step S 258 , where an automatic return to the standard mode is made, and the flow ends. On the other hand, if, at step S 256 , no movement acceleration is detected, the currently set mode is maintained, and the flow ends. If, at step S 256 , movement acceleration is detected, it can indicate that, for example, a person who was sitting on a chair and reading a book or doing handwork has stood up and started to walk, and maintaining the enlargement mode or the white-black reversal mode in such a situation can be dangerous; therefore, at step S 258 , an automatic return to the standard mode is made. The standard mode is the real-scale mode or the wide mode set at step S 234  or S 238 . The standard mode may be custom-set beforehand to suit a particular user. 
         [0114]    The various features of the examples described above are not limited to those particular embodiments, but may be implemented in any other embodiments so long as they provide their benefits. Although in the present description, for simplicity&#39;s sake, the description and illustration of each embodiment concentrate on features different from the other embodiments, needless to say, embodiments are also possible where features described in connection with different embodiments coexist, where those features are replaced with other features, or where a plurality of features are combined together. 
       Example 4 
       [0115]      FIG. 11  is a block diagram showing the overall configuration of a vision aid system in Example 4 embodying the present invention. The configuration of Example 4 in  FIG. 11  has much in common with Example 1 in  FIG. 1 ; accordingly, the same parts are identified with the same reference signs, and no overlapping description will be repeated. A first difference of Example 4 from Example 1 is that it is configured to be usable without the use of ordinary eyeglasses  10 . That is, adjustment of the dioptric power for near-sightedness and far-sightedness is achieved through adjustment of the focus of the right-eye and left-eye eyepiece optical systems  18  and  20 ; astigmatism is corrected with a right-eye toric lens  76  and a left-eye toric lens  78  which are removably inserted. The right-eye and left-eye toric lenses  76  and  78  are individually interchangeable to suit the user&#39;s dioptric power, and are removable whenever unnecessary. With the right-eye and left-eye toric lenses  76  and  78  inserted, they are rotated about the lines of sight  6   a  and  8   a  respectively to achieve correction that suits the axial angle of the user&#39;s astigmatism. A second difference of Example 4 from Example 1 is that a central controller  80  and an image processor  81  execute unique functions, which will be described later. 
         [0116]      FIGS. 12A to 12C  are schematic sectional diagrams explaining the principle of dioptric power adjustment for near-sightedness or far-sightedness in the eyepiece optical systems  18  and  20  in Example 4. For simplicity&#39;s sake, illustration and description will be given only for the right eye  6 , and the same apply equally to the left eye  8 . In  FIG. 12A , an eyepiece lens  18   a  in the right-eye eyepiece optical system  18  is movable for dioptric power adjustment between a display surface  12   a  and the right eye  6  along the right-eye line of sight  6   a.  In the state in  FIG. 12A , the eyepiece lens  18   a  is set at a standard position. In this state, the virtual image  12   b  of the display surface  12   a  is located within a visual acuity range  82  of the visually healthy. On the other hand, in the state in  FIG. 12A , the position of the virtual image  12   b  of the display surface  12   a  falls outside either of a visual acuity range  84  of the near-sighted and a visual acuity range  86  of the far-sighted. 
         [0117]    In  FIG. 12B , the dioptric power has been adjusted by shifting the eyepiece lens  18   a  toward the display surface  12   a  so that the display virtual image  12   c  is located within the visual acuity range  84  of the near-sighted. In  FIG. 12C , the dioptric power has been adjusted by shifting the eyepiece lens  18   a  toward the right eye  6  so that the display virtual image  12   d  is located within the visual acuity range  86  of the far-sighted. 
         [0118]      FIGS. 13A to 13C  to  FIGS. 19A to 19C  are diagrams explaining the relationship between parallax and convergence angle as observed mainly in the imaging and displaying of a 3D (three-dimensional) image, based on a study of different states in Example 4 in relation to the relationship in  FIGS. 12A to 12C  respectively. As will be described in detail below, in Example 4, an imaging system and a display system are each configured to fulfill predetermined conditions so that 3D display is possible with hardly any sense of unnaturalness over the entire ranges of dioptric power adjustment for near- and far-sightedness, of object distance change, and of enlargement and reduction (widening where a peripheral image is involved) of the display image. In  FIGS. 13A to 13C  to  FIGS. 17A to 17C , for simplicity&#39;s sake, a single object point and the eyes&#39; convergence angle are studied; in  FIGS. 18A to 18B  and  FIGS. 19A to 19B , the reality of vision based on the convergence angle is studied with the displayed image enlarged and reduced, respectively. The process by which the brain recognizes a 3D image depends not only on one element like the eyes&#39; convergence angle with respect to a single object point but also greatly on, for example, parallax information on a plurality of object points at different distances. However, the elements studied do not contradict the results of comprehensive 3D recognition by eye movement and the brain. 
         [0119]      FIGS. 13A to 13C  show the basic configuration for imaging and displaying a 3D image in Example 4.  FIG. 13A  shows the basic configuration of a parallel binocular imaging system composed of a right-eye deflecting zoom lens optical system  24  and a left-eye deflecting zoom lens optical system  28 . For simplicity&#39;s sake, the optical paths that are bent in reality are illustrated as straightened optical paths that are equivalent to them. As will be clear from  FIG. 13A , the optical axes (indicated by broken lines) of the right-eye and left-eye deflecting zoom lens optical systems  24  and  28  are parallel to each other, and their interval (axis-to-axis interval, referred to as an optical axis interval) is set at an average human interpupillary distance. Moreover, the right-eye and left-eye deflecting zoom lens optical systems  24  and  28  are both set at a standard focal length, and their foci are adjusted to be on an object point  88  located at a standard distance. The standard distance of the object point  88  is set equal to the distance of the position of the virtual image  12   b  of the display surface  12   a  in  FIG. 12A . In this configuration, parallax arises with respect to the object point  88  as seen from the right-eye and left-eye deflecting zoom lens optical systems  24  and  28 , and thus the image point  90  imaged on the imaging surface  22   a  of the right-eye image sensor  22  and the image point  92  imaged on the imaging surface  26   a  of the right-eye image sensor  26  are located at positions displaced from the respective optical axes in the opposite directions. This is imaged, as parallax information on the object point  88 , by the right-eye and left-eye image sensors  22  and  26 . 
         [0120]    In  FIG. 13B , by use of a parallel binocular display of which the interpupillary distance equals the interval between the optical axes of parallel binocular lenses (the right-eye and left-eye deflecting zoom lens optical systems  24  and  28 ), image information imaged by the right-eye and left-eye image sensors  22  and  26  in  FIG. 13A  are displayed on the right-eye and left-eye display surfaces  12   a  and  14   a  respectively. In  FIG. 13B , the positions of the right-eye display surface  12   a  and the right-eye eyepiece lens  18   a  are set as in  FIG. 12A , and so are the positions of the left-eye display surface  14   a  and the left-eye eyepiece lens  20   a.  Thus, the virtual image  12   b  of the display surface  12   a  and the virtual image  14   b  of the display surface  14   a  are seen at the same position. 
         [0121]    Moreover, in  FIG. 13A , the image point  90  imaged on the imaging surface  22   a  and the image point  92  imaged on the imaging surface  26   a  are both real images that are each inverted upside down and reversed left to right. Accordingly, when these images are displayed on the right-eye and left-eye display surfaces  12   a  and  14   a  and their virtual images are observed, they are displayed each 180 degrees rotated upside down and left to right to appear as erect images. As a result, the image information of the image points  90  and  92  on the imaging surfaces  22   a  and  26   a  is displayed as display points  94  and  96 , respectively, on the right-eye and left-eye display surfaces  12   a  and  14   a.    
         [0122]    In this way, the right-eye and left-eye display surfaces  12   a  and  14   a  on which the display points  94  and  96  are respectively displayed are observed, through the right-eye and left-eye eyepiece lenses  18   a  and  20   a,  as the virtual images  12   b  and  14   b  of the display surfaces on which virtual-image display points  94   a  and  96   a  are respectively displayed. Here, the central controller  80  controls the image processor  81  to perform shift adjustment on the display points  94  and  96  so that the virtual-image display points  94   a  and  96   a  coincide.  FIG. 13B  shows a state where, as a result of the right and left eyes  6  and  8  gazing at the virtual-image display points  94   a  and  96   a  described above, real images  94   b  and  96   b  of the virtual-image display points  94   a  and  96   a  are imaged at the centers of the retinae of the right and left eyes  6  and  8  respectively. The gaze produces a convergence angle between the right and left eyes  6  and  8 , and produces the sense of distance to the coincident virtual-image display points  94   a  and  96   a.    
         [0123]      FIG. 13C  shows a state of the convergence angle between the right and left eyes  6  and  8  as observed when a visually healthy person really sees the object point  88  in FIG.  13 A with naked eyes. The convergence angle in  FIG. 13B  approximately equals that in  FIG. 13C , and thus observation in  FIG. 13B  gives the user the same perception as does observation in  FIG. 13C . The description thus far concerns with a visually healthy person, and corresponds, in terms of visual acuity range, the state described with reference to  FIG. 12A . 
         [0124]    In  FIGS. 14A and 14B , a similar study is done in Example 4 with a near-sighted person. As explained with reference to  FIG. 12A , the virtual images  12   b  and  14   b  of the right-eye and left-eye display surfaces  12   a  and  14   a  in the state in  FIG. 13B  are both located outside the visual acuity range  84  of the near-sighted, and cannot be seen clearly. Accordingly, in  FIG. 14A , as in  FIG. 12B , the dioptric power is adjusted by shifting the right-eye and left-eye eyepiece lenses  18   a  and  20   a  toward the right-eye and left-eye display surfaces  12   a  and  14   a  so that the virtual images  12   c  and  14   c  of the right-eye and left-eye display surfaces  12   a  and  14   a  are both located within the visual acuity range  84  of the near-sighted. The right-eye and left-eye display surfaces  12   a  and  14   a  and the display points  94  and  96  displayed on them are the same as those in  FIG. 13B . 
         [0125]    In  FIG. 14A , as in  FIG. 12B , the virtual image  12   c  of the display surface  12   a  on which the display point  94  is displayed and the virtual image  14   c  of the display surface  14   a  on which the display point  96  is displayed are closer to the right and left eyes  6  and  8  respectively, and are located within the visual acuity range  84  of the near-sighted. However, at this time, virtual-image display points  94   c  and  96   c  that appear to be displayed on the virtual images  12   c  and  14   c  of the right-eye and left-eye display surfaces  12   a  and  14   a  respectively do not coincide on the virtual images  12   c  and  14   c  located within the visual acuity range  84 . However, trying to see the virtual-image display points  94   c  and  96   c  as coincident points, the right and left eyes  6  and  8  assume a convergence angle that permits the real images  94   b  and  96   b  of the virtual-image display points  94   c  and  96   c  to be imaged at the centers of the retinae of the right and left eyes  6  and  8  respectively. As a result, what is being seen is perceived as coincident points  94   d  and  96   d.    
         [0126]      FIG. 14B  shows a state of the convergence angle between the right and left eyes  6  and  8  as observed when a near-sighted person really sees the object point  88  in  FIG. 13A  with concave-lens glasses  98  worn for correction in everyday life. The convergence angle in  FIG. 14A  approximately equals the convergence angle in  FIG. 14B , and thus observation of the coincident points  94   d  and  96   d  in  FIG. 14A , where the dioptric power is adjusted for the naked eye, gives the user the same perception as does observation of the object point  88  with glasses  98  worn in everyday life as in  FIG. 14B . Strictly speaking, the positions of the coincident points  94   d  and  96   d  in  FIG. 14A  differ from those of the virtual-image display points  94   a  and  96   a  in  FIG. 13B , but because the difference is slight, it is possible to omit shifting and correcting the positions of the display points  94  and  96  displayed on the right-eye and left-eye display surfaces  12   a  and  14   a  according to dioptric power adjustment between  FIGS. 13B and 14B . 
         [0127]    In  FIGS. 15A and 15B , a similar study is done in Example 4 with a far-sighted person. As explained with reference to  FIG. 12A , the virtual images  12   b  and  14   b  of the right-eye and left-eye display surfaces  12   a  and  14   a  in the state in  FIG. 13B  are both located outside the visual acuity range  86  of the far-sighted, and cannot be seen clearly. Accordingly, in  FIG. 15A , as in  FIG. 12C , the dioptric power is adjusted by shifting the right-eye and left-eye eyepiece lenses  18   a  and  20   a  toward the right and left eyes  6  and  8  so that the virtual images  12   d  and  14   d  of the right-eye and left-eye display surfaces  12   a  and  14   a  are both located within the visual acuity range  86  of the far-sighted. The right-eye and left-eye display surfaces  12   a  and  14   a  and the display points  94  and  96  displayed on them are the same as those in  FIG. 13B . 
         [0128]    In  FIG. 15A , as in  FIG. 12C , the virtual image  12   d  of the display surface  12   a  on which the display point  94  is displayed and the virtual image  14   d  of the display surface  14   a  on which the display point  96  is displayed are farther away from the right and left eyes  6  and  8  respectively, and are located within the visual acuity range  86  of the far-sighted. However, at this time, virtual-image display points  94   e  and  96   e  that appear to be displayed on the virtual images  12   d  and  14   d  of the right-eye and left-eye display surfaces  12   a  and  14   a  respectively do not coincide on the virtual images  12   d  and  14   d  located within the visual acuity range (their positions are crossed and reversed relative to each other). However, trying to see the virtual-image display points  94   e  and  96   e  as coincident points, the right and left eyes  6  and  8  assume a convergence angle that permits the real images  94   b  and  96   b  of the virtual-image display points  94   e  and  96   e  to be imaged at the centers of the retinae of the right and left eyes  6  and  8  respectively. As a result, what is being seen is perceived as coincident points  94   f  and  96   f    
         [0129]      FIG. 15B  shows a state of the convergence angle between the right and left eyes  6  and  8  as observed when a far-sighted person really sees the object point  88  in  FIG. 13A  with convex-lens glasses  100  worn for correction in everyday life. The convergence angle in  FIG. 15A  too approximately equals the convergence angle in  FIG. 15B , and thus observation of the coincident points  94   f  and  96   f  in  FIG. 15A , where the dioptric power is adjusted for the naked eye, gives the user the same perception as does observation of the object point  88  with glasses  100  worn in everyday life as in  FIG. 15B . Strictly speaking, the positions of the coincident points  94   f  and  96   f  in  FIG. 15A  differ from those of the virtual-image display points  94   a  and  96   a  in  FIG. 13B , but, as with near-sightedness, it is possible to omit shifting and correcting the positions of the display points  94  and  96  displayed on the right-eye and left-eye display surfaces  12   a  and  14   a  according to dioptric power adjustment. 
         [0130]    The above has been a description of how a visually healthy person, a short-sighted person, and a long-sighted person see the display on the right-eye and left-eye display surfaces  12   a  and  14   a  based on the same image information taken in  FIG. 13A . As described above, in Example 4, parallax information on the object point  88  is obtained by a parallel binocular imaging system of which the interval is set at an average human interpupillary distance. Then, the image information including the parallax information is displayed on a parallel binocular display of which the interpupillary distance equals the interval between the optical axes of the parallel binocular imaging system so that, with the convergence angle of the eyes trying to see the object points on the right and left display at coincident points, binocular vision is achieved. Then, through dioptric power adjustment, a short- or long-sighted person is coped with so as to be presented with reproduction similar to that presented to a visually healthy person. 
         [0131]    Next, with reference to  FIGS. 16A to 16C  and  FIGS. 17A to 17C , a description will be given of a case where the position of an object point differs from that of the object point  88  set equal to the distance of the position of the virtual image  12   b  of the display surface  12   a.  For simplicity&#39;s sake, only a visually healthy person will be dealt with. As for a short- or long-sighted person, an understanding will be obtained similarly with reference to  FIGS. 14A and 14B  and  FIGS. 15A and 15B . 
         [0132]      FIGS. 16A to 16C , though similar to  FIGS. 13A to 13C , show a case where, as shown in  FIG. 16A , the foci of the right-eye and left-eye deflecting zoom lens optical systems  24  and  28  are so adjusted as to be on a close object point  102  which is closer than the object point  88  at the standard distance in  FIG. 13A . As will be described later, the close object point  102  is assumed to be located within the visual acuity range of a visually healthy person. In this state, the parallax with respect to the close object point  102  as seen from the right-eye and left-eye deflecting zoom lens optical systems  24  and  28  is larger than in the case shown in  FIG. 13A , and thus the positions of the image points  104  and  106  imaged on the imaging surfaces  22   a  and  26   a  of the right-eye and left-eye image sensors  22  and  26  are displaced greatly from the respective optical axes in the opposite directions. This is imaged, as parallax information on the close object point  102 , by the right-eye and left-eye image sensors  22  and  26 . 
         [0133]    In  FIG. 16B , the image information imaged by the right-eye and left-eye image sensors  22  and  26  in the state in  FIG. 16A  is displayed on the right-eye and left-eye display surfaces  12   a  and  14   a  respectively. In  FIG. 16B , the positions of the right-eye display surface  12   a  and the right-eye eyepiece lens  18   a  are set similarly as in  FIG. 12A , and so are the positions of the left-eye display surface  14   a  and the left-eye eyepiece lens  20   a.  In this respect,  FIG. 16B  is the same as  FIG. 13B . 
         [0134]    However, due to the close object point  102  being closer, the display points  108  and  110  displayed on the right-eye and left-eye display surfaces  12   a  and  14   a  are displaced greatly from the center of display in the opposite directions. Accordingly, when the right-eye and left-eye display surfaces  12   a  and  14   a  on which those display points  108  and  110  are respectively displayed are seen through the right-eye and left-eye eyepiece lenses  18   a  and  20   a  as virtual images  12   b  and  14   b  of the right-eye and left-eye display surfaces  12   a  and  14   a  respectively, the virtual-image display points  108   a  and  110   a  on the virtual images do not coincide (their positions are crossed and reversed relative to each other). However, trying to see those virtual-image display points  108   a  and  110   a  as coincident points, the right and left eyes  6  and  8  assume such a tense (large) convergence angle that real images  108   b  and  110   b  of the virtual-image display points  108   a  and  110   a  are imaged at the centers of the retinae of the right and left eyes  6  and  8 . As a result, what is seen is perceived to be coincident points  108   c  and  110   c  located at a closer distance. 
         [0135]      FIG. 16C  shows a state of the convergence angle of the right and left eyes  6  and  8  as observed when a visually healthy person really sees the close object point  102  in  FIG. 16A  with naked eyes. As mentioned above, the close object point  102  is located within the visual acuity range of the visually healthy. The convergence angle in  FIG. 16B  approximately equals the convergence angle in  FIG. 16C , and thus observation of the coincident points  108   c  and  110   c  in  FIG. 16B  gives the user the same perception as does observation of the close object point  102  in  FIG. 16C . 
         [0136]      FIGS. 17A to 17C , though similar to  FIGS. 13A to 13C  and to  FIGS. 16A to 16C , show a case where, as shown in  FIG. 17A , the foci of the right-eye and left-eye deflecting zoom lens optical systems  24  and  28  are so adjusted as to be on a far object point  112  which is farther away than the object point  88  at the standard distance in  FIG. 13A . The far object point  112  too is assumed to be located within the visual acuity range of a visually healthy person. In this state, the parallax with respect to the far object point  112  as seen from the right-eye and left-eye deflecting zoom lens optical systems  24  and  28  is smaller than in the case shown in  FIG. 13A , and thus the positions of the image points  114  and  116  imaged on the imaging surfaces  22   a  and  26   a  of the right-eye and left-eye image sensors  22  and  26  are, though displaced, closer to the optical axes. This is imaged, as parallax information on the far object point  112 , by the right-eye and left-eye image sensors  22  and  26 . 
         [0137]    In  FIG. 17B , the image information imaged by the right-eye and left-eye image sensors  22  and  26  in the state in  FIG. 17A  is displayed on the right-eye and left-eye display surfaces  12   a  and  14   a  respectively. In  FIG. 17B , the positions of the right-eye display surface  12   a  and the right-eye eyepiece lens  18   a  are set similarly as in  FIG. 12A , and so are the positions of the left-eye display surface  14   a  and the left-eye eyepiece lens  20   a.  In this respect,  FIG. 17B  is the same as  FIG. 13B and 16B . 
         [0138]    However, due to the far object point  112  being farther away, the display points  118  and  120  displayed on the right-eye and left-eye display surfaces  12   a  and  14   a  are closer to the center of display. Accordingly, when the right-eye and left-eye display surfaces  12   a  and  14   a  on which those display points  118  and  120  are respectively displayed are seen through the right-eye and left-eye eyepiece lenses  18   a  and  20   a  as virtual images  12   b  and  14   b  of the right-eye and left-eye display surfaces  12   a  and  14   a  respectively, the virtual-image display points  118   a  and  120   a  on the virtual images do not coincide. However, trying to see those virtual-image display points  118   a  and  120   a  as coincident points, the right and left eyes  6  and  8  assume such a slack (small) convergence angle that real images  118   b  and  120   b  of the virtual-image display points  118   a  and  120   a  are imaged at the centers of retinae of the right and left eyes  6  and  8 . As a result, what is seen is perceived to be coincident points  118   c  and  120   c  located at a farther distance. 
         [0139]      FIG. 17C  shows a state of the convergence angle of the right and left eyes  6  and  8  as observed when a visually healthy person really sees the far object point  112  in  FIG. 17A  with naked eyes. As mentioned above, the far object point  112  is located within the visual acuity range of the visually healthy. The convergence angle in  FIG. 17B  approximately equals the convergence angle in  FIG. 17C , and thus observation of the coincident points  118   d  and  120   d  in  FIG. 17B  gives the user the same perception as does observation of the far object point  112  in  FIG. 17C . 
         [0140]    The configuration of Example 4, where image information imaged by a parallel binocular imaging system having mutually parallel optical axes of which the interval is set at an average human interpupillary distance is respectively displayed on a parallel binocular display of which the interpupillary distance equals the interval between the optical axes of the parallel binocular imaging system, achieves binocular vision with respect to objects at varying distances owing to the convergence angle of the eyes trying to see object points on right and left display as coincident points. 
         [0141]      FIGS. 18A and 18B  and  FIGS. 19A and 19B  are directed to cases where the central controller  80  controls the image processor  81  so as to enlarge and reduce (widen), respectively, the display images on the right-eye and left-eye display surfaces  12   a  and  14   a,  and show a study on the reality of vision obtained where enlargement and reduction are involved from the viewpoint of the convergence angle. 
         [0142]      FIGS. 18A and 18B  are directed to a case where the display images on the right-eye and left-eye display surfaces  12   a  and  14   a  are each enlarged. First,  FIG. 18A  shows a standard-magnification state before enlargement, corresponding to the state in  FIG. 13B . Here, display images  122  and  124  are displayed on the right-eye and left-eye display surfaces  12   a  and  14   a  respectively (to illustrate the effect of enlargement and reduction, instead of points, dimensional images (hollow arrows) are shown here). As in  FIG. 13B , the right-eye and left-eye display surfaces  12   a  and  14   a  on which the display images  122  and  124  are displayed are seen through the right-eye and left-eye eyepiece lenses  18   a  and  20   a  as virtual images  12   b  and  14   b  of the right-eye and left-eye display surfaces  12   a  and  14   a  on which the virtual-image display images  122   a  and  124   a  are displayed respectively. Here, as in  FIG. 13B , the virtual-image display images  122   a  and  124   a  coincide.  FIG. 18A  shows a state where, as a result of the right and left eyes  6  and  8  gazing at those virtual-image display images  122   a  and  124   a,  real images  122   b  and  124   b  (of which only the positions are indicated by dots) of the virtual-image display images  122   a  and  124   a  are imaged at the centers of the retinae of the right and left eyes  6  and  8 . As in  FIG. 13B , the gaze produces the convergence angle between the right and left eyes  6  and  8 , and produces the sense of distance to the coincident virtual-image display points  122   a  and  124   a.    
         [0143]    In contrast,  FIG. 18B  shows a case where the display images on the right-eye and left-eye display surfaces  12   a  and  14   a  are enlarged into enlarged display images  126  and  128  respectively. What is important here is, instead of enlarging the enlarged display images  126  and  128  themselves about their respective centers, to enlarge the entire images about central parts of the entire right t-eye and left-eye display surfaces  12   a  and  14   a.  Consequently, when the display images  122  and  124 , which were not in central parts of the entire right-eye and left-eye display surfaces  12   a  and  14   a  in the state in  FIG. 18A , become the enlarged display images  126  and  128  in  FIG. 18B , they are not only enlarged but are also farther displaced to the opposite sides (away from the central parts of the respective display surfaces). 
         [0144]    Accordingly, when the right-eye and left-eye display surfaces  12   a  and  14   a  on which the enlarged display images  126  and  128  are displayed are seen through the right-eye and left-eye eyepiece lenses  18   a  and  20  as the virtual images  12   b  and  14   b  of the right-eye and left-eye displays  12  and  14  respectively, virtual-image enlarged display images  126   a  and  128   a  on the virtual images do not coincide (their positions are crossed and reversed relative to each other). However, trying to see the virtual-image enlarged display images  126   a  and  128   a  as coincident points, the right and left eyes  6  and  8  assume such a tense (large) convergence angle that real images  126   b  and  128   b  (of which only the positions are indicated by dots) of the virtual-image enlarged display images  126   a  and  128   a  are imaged at the centers of the retinae of the right and left eyes  6  and  8  respectively. As a result, what is seen is perceived to be coincident images  126   c  and  128   c  located at a closer distance. Thus, the coincident images  126   c  and  128   c  are enlarged and in addition appear closer, providing the reality of a 3D (three-dimensional) image. 
         [0145]    On the other hand,  FIGS. 19A and 19B  are directed to a caser where the display images on the right-eye and left-eye display surfaces  12   a  and  14   a  are reduced (or, in a case where there is a peripheral image, widened).  FIG. 19A  is the same as  FIG. 18A , showing the standard magnification state before reduction. 
         [0146]    In contrast,  FIG. 19B  shows a case where the display images on the right-eye and left-eye display surfaces  12   a  and  14   a  are reduced into reduced display images  130  and  132  respectively. What is important here as in  FIG. 18B  is, instead of reducing the reduced display images  130  and  132  themselves about their respective centers, to reduce the entire images about central parts of the entire right-eye and left-eye display surfaces  12   a  and  14   a.  Consequently, when the display images  122  and  124  in the state in  FIG. 19A  become the reduced display images  130  and  132  in  FIG. 19B , they are not only reduced but also come closer to the central parts of the respective display surfaces. 
         [0147]    Accordingly, when the right-eye and left-eye display surfaces  12   a  and  14   a  on which the reduced display images  130  and  132  are displayed are seen through the right-eye and left-eye eyepiece lenses  18   a  and  20  as the virtual images  12   b  and  14   b  of the right-eye and left-eye displays  12  and  14  respectively, virtual-image reduced display images  130   a  and  132   a  on the virtual images do not coincide. However, trying to see the virtual-image reduced display images  130   a  and  132   a  as coincident points, the right and left eyes  6  and  8  assume such a slack (small) convergence angle that real images  130   b  and  132   b  (of which only the positions are indicated by dots) of the virtual-image reduced display images  130   a  and  132   a  are imaged at the centers of the retinae of the right and left eyes  6  and  8  respectively. As a result, what is seen is perceived to be coincident images  130   c  and  132   c  located at a farther distance. Thus, the coincident images  130   c  and  132   c  are reduced and in addition appear farther away, providing the reality of a 3D image. 
         [0148]      FIGS. 20A to 20C  to  FIGS. 22A to 22C  explain the parallax and the convergence angle observed in a case employing an imaging system and a display system that are in a different relationship with each other than under the conditions described with reference to  FIGS. 13A to 13C  to  FIGS. 19A to 19B . 
       Example 5 
       [0149]      FIGS. 20A to 20C  are schematic sectional views of Example 5 embodying the present invention. In Example 5 shown in  FIGS. 20A to 20C  to  FIGS. 22A to 22C , image information taken by a compact parallel binocular imaging system having mutually parallel optical axes of which the interval is set smaller than an average human interpupillary distance is respectively displayed on a parallel binocular display of which the interval is set equal to an average human interpupillary distance. To follow is a description of processing in Example 5, where, as just mentioned, the parallel binocular imaging system and the parallel binocular display system have different optical axis intervals. Example 5 shares other features with Example 4, and accordingly, for detailed features,  FIG. 11  is to be referred to auxiliarily. 
         [0150]      FIG. 20A  shows the basic configuration of a 3D parallel binocular imaging system composed of a right-eye deflecting zoom lens optical system  134  and a left-eye deflecting zoom lens optical system  136 . As in  FIG. 13A , for simplicity&#39;s sake, the optical paths are illustrated in a straightened form. As in Example 4, the optical axes of the right-eye and left-eye deflecting zoom lens optical systems  134  and  136  are parallel to each other, and their interval is smaller than an average human interpupillary distance. Incidentally, the right-eye and left-eye deflecting zoom lens optical systems  134  and  136  are both set at a standard focal distance, and their foci are so adjusted to be on an object point  88  located at a standard distance. The standard distance of the object point  88  is set equal to the distance of the position of the virtual image  12   b  of the right-eye display surface  12   a.    
         [0151]    The image points  142  and  144  imaged by those right-eye and left-eye deflecting zoom lens optical systems  134  and  136  on the imaging surfaces  138   a  and  140   a  of right-eye and left-eye image sensors are displaced from the respective optical axes in the opposite directions. However, the displacements are smaller than in  FIG. 13A  because the right-eye and left-eye deflecting zoom lens optical systems  134  and  136  have smaller optical axis intervals. 
         [0152]      FIG. 20B  shows a parallel binocular display of which the interpupillary distance equals an average human interpupillary distance as described above, configured as in  FIG. 13B . However, if display on the right-eye and left-eye display surfaces  12   a  and  14   a  is performed based on image information in which the displacements of the image points  142  and  144  are small as in  FIG. 20A , the display points  146  and  148  are closer to the centers of the respective display surfaces. Thus, when the right-eye and left-eye display surfaces  12   a  and  14   a  on which those display points  146  and  148  are displayed are seen as virtual images  12   b  and  14   b  of the right-eye and left-eye display surfaces  12   a  and  14   a,  virtual-image display points  146   a  and  148   a  do not coincide. Trying to see the virtual-image display points  146   a  and  148   a  as coincident points, the right and left eyes  6  and  8  assume such a slack (small) convergence angle that their real images  146   b  and  148   b  are imaged at the centers of the retinae of the right and left eyes  6  and  8 . As a result, what is seen is perceived to be coincident points  146   c  and  148   c  located farther away than the object point  88 . In this way, in a case where the optical axis intervals of the parallel binocular imaging system and the parallel binocular display system are not equal, the displayed coincident points  146   c  and  148   c  appear to be seen at a distance different from that of the object point  88  as the imaging target, and produces a sense of unnaturalness. 
         [0153]      FIG. 20C  shows a configuration for eliminating the sense of unnaturalness mentioned above. Specifically, as shown in  FIG. 20C , the central controller  80  controls the image processor  81  so as to shift the display points on the right-eye and left-eye display surfaces  12   a  and  14   a  so that virtual-image display points  150   d  and  152   d  coincide on the virtual images  12   b  and  14   b  of the right-eye and left-eye display surfaces  12   a  and  14   a.  That is, as indicated by arrows in  FIG. 20C , the display points  146  and  148  shown in  FIG. 20B  are shifted outward relative to the respective display surfaces up to display points  150  and  152  so that the virtual-image display points  150   d  and  152   d  coincide on the virtual images  12   b  and  14   b  of the right-eye and left-eye display surfaces  12   a  and  14   a.  Now, the state of the convergence angle is such that the displayed coincident points (virtual-image display points  150   d  and  152   d ) are seen at the same position as that of the object point  88  as the imaging target, producing no sense of unnaturalness. 
       Example 6 
       [0154]      FIGS. 21A to 21C  are schematic sectional view of Example 6 embodying the present invention. In Example 6, a parallel binocular display is configured to have an adjustable interpupillary distance. Specifically, in Example 6 shown in  FIGS. 21A to 21C , image information taken by a compact parallel binocular imaging system having mutually parallel optical axes of which the interval is set smaller than an average human interpupillary distance is respectively displayed on a parallel binocular display of which the interpupillary distance is adjustable. 
         [0155]      FIG. 21A  is the same as  FIG. 20A . That is, also in Example 6, the interval between the optical axes of the right-eye and left-eye deflecting zoom lens optical systems  134  and  136  is smaller than an average human interpupillary distance, and the displacements of the image points  142  and  144  imaged on the imaging surfaces  138   a  and  140   a  of right-eye and left-eye image sensors are smaller than in  FIG. 13A  because the right-eye and left-eye deflecting zoom lens optical systems  134  and  136  have a smaller optical axis interval. 
         [0156]      FIG. 21B  is a schematic sectional view of a parallel binocular display similar to that in  FIG. 20B , and here, through interpupillary distance adjustment, the left-eye display surface  14   a  and the left-eye eyepiece lens  20   a  are brought closer to the right-eye display surface  12   a  and the right-eye eyepiece lens  18   a  respectively, so that the interpupillary distance of the parallel binocular display equals the interval between the optical axes of the parallel binocular imaging system. This state is suitable for a display for children with smaller interpupillary distances. As a result of the distances between the optical axes of the parallel binocular imaging system and of the parallel binocular display system being made equal, the relationship between  FIGS. 21A and 21B  is similar to the relationship between  FIGS. 13A and 13B , and the virtual-image display points  146   a  and  148   a  on the virtual images  12   b  and  14   b  of the right-eye and left-eye display surfaces  12   a  and  14   a  coincide. Their positions appear to be at the same distance as that of the object point  88  as the imaging target, and no sense of unnaturalness is produced. In this way, a sense of unnaturalness can be eliminated also through adjustment of the optical axis interval. 
         [0157]      FIG. 21C  is the same as  FIG. 20C , and shows a case where, through interpupillary distance adjustment, the interpupillary distance has been increased, for example, for adults. In this case, as in Example 5, the central controller  80  controls the image processor  81  so as to shift the display points on the right-eye and left-eye display surfaces  12   a  and  14   a,  and thereby eliminates a sense of unnaturalness. 
       Example 7 
       [0158]      FIGS. 22A to 22C  are schematic sectional views of Example 7 embodying the present invention. Example 7 has a parallel binocular imaging system and a parallel binocular display configured as separate units, and is suitable in cases where one of different types of parallel binocular imaging systems and one of different types of parallel binocular displays are combined together. 
         [0159]      FIG. 22A  shows a parallel binocular display used in a basic combination, and its configuration is the same as in  FIG. 21B . However, here, the interpupillary distance is fixed at a small distance. In the basic combination of Example 7, the parallel binocular display in  FIG. 22A  is combined with the parallel binocular imaging system shown in  FIG. 21A . This combination is equivalent to the relationship between  FIGS. 21B and 21A , and thus produces no sense of unnaturalness. 
         [0160]      FIG. 22B  shows another parallel binocular display that can be combined with the parallel binocular imaging system shown in  FIG. 21A . The optical axis interval of the parallel binocular display in  FIG. 22B  is equal to that of the parallel binocular imaging system, but here, right-eye and left-eye display surfaces  154   a  and  156   a  are located at positions far away from the right and left eyes  6  and  8 , and right-eye and left-eye eyepiece lenses  158   a  and  160   a  have accordingly different optical systems. Thus, in this combination, the relationship between the parallel binocular imaging system and the parallel binocular display is similar to that between  FIGS. 20A and 20B . Thus, as shown in  FIG. 22C , correction as in  FIG. 20C  is performed to eliminate a sense of unnaturalness. To that end, whatever parallel binocular imaging system and parallel binocular display used hold information necessary for correction and communicate it to each other. 
         [0161]    The various features of the examples described above provide their benefits without being limited to those particular embodiments. 
         [0162]    For example, the various features of those examples which are configured as a vision aid system in which a binocular imaging system and a binocular display device are integrated together and which allows real-time viewing of the visual field before the eyes may be applied to a configuration where, as in Example 7, a binocular imaging system and a binocular display device are configured as separate units comprising a 3D camera and a 3D head-mounted display respectively. It is thereby possible to build a system that allows 3D movie content taken by the 3D camera to be viewed at different times and/or at different places through the 3D head-mounted display. 
         [0163]    To follow is a comprehensive description of the various examples described above. 
         [0164]    According to one aspect of the examples disclosed herein, a vision aid system is provided that includes: an imager which images a target that a user intends to see; an image processor which corrects an image obtained by the imager to suit the user&#39;s vision disorder; a display which displays the image from the image processor so that the user sees it; a light transmitter through which the user directly sees a target outside the display that the user intends to see; and a controller which controls the light transmitter in a manner corresponding to the image processing by the image processor. This makes it possible to match the image on the display with the target seen directly through the light transmitter. 
         [0165]    According to a specific feature, the light transmitter is controlled according to the brightness of the display. According to another specific feature, the light transmitter can be controlled both according to the brightness of the display and irrespective of the brightness of the display. According to another specific feature, the light transmitter is light-shielded when the display is white-black reversed. 
         [0166]    According to another specific feature, the image processor compensates for a pupil reaction. According to another specific feature, the controller which controls the light transmitter compensates for a pupil reaction. These features make possible control with a pupil reaction taken into consideration. 
         [0167]    According to another aspect of the examples disclosed herein, a vision aid system is provided that includes: an imager which images a target that a user intends to see; an image processor which corrects an image obtained by the imager to suit the user&#39;s vision disorder; a display which displays the image from the image processor so that the user sees it; and a memory which stores preset information on correction in the image processor. Here, the preset information is definitively determined by averaging a plurality of values judged to be optimal. This makes it possible to determine appropriate preset values definitively. According to a specific feature, the preset information is stored separately for the right and left eyes. 
         [0168]    According to another aspect of the examples disclosed herein, a vision aid system is provided that includes: an imager which images a target that a user intends to see; an image processor which corrects an image obtained by the imager to suit the user&#39;s vision disorder; and a display which displays the image from the image processor so that the user sees it. Here, the image processor can display an image on the display on an enlarged scale, and delays movement of the displayed image when enlargement higher than a predetermined magnification is performed. This alleviates the sense of unnaturalness felt in viewing an enlarged image. 
         [0169]    According to another aspect of the examples disclosed herein, a vision aid system is provided that includes: an imager which images a target that a user intends to see; and a display which displays the image obtained by the imager so that the user sees it. Here, the optical axis of the imager and the optical axis of the display coincide with each other. This provides a vision aid system that is comfortable to see with. According to a specific feature, a controller is further included which displaces the optical axis of the imager and the optical axis of the display from each other. This makes it possible to cope with a variety of vision disorders. 
         [0170]    According to another aspect of the examples disclosed herein, a vision aid system is provided that includes: a pair of imagers, one for each eye, which images a target that a user intends to see; and a pair of displays, one for each eye, which displays the images from the pair of imagers, respectively, so that the user sees them. Here, the pair of imagers and the pair of displays are arranged so as not to intercept outside the visual field of the two eyes. This makes it possible to obtain information outside the visual field effectively. According to a specific feature, each of the pair of imagers is bent inward of the two eyes. According to another specific feature, the pair of imagers are arranged so as not to protrude frontward. 
         [0171]    According to another aspect of the examples disclosed herein, a vision aid system is provided that includes: an imager which images a target that a user intends to see; an image processor which corrects an image obtained by the imager to suit the user&#39;s vision disorder; a display which displays the image from the image processor so that the user sees it; a memory which stores a plurality of processing modes by the image processor; and a selector which selects among the plurality of processing modes. This makes it possible to select a processing mode that suits the circumstances of use. 
         [0172]    According to a specific feature of the examples disclosed herein, a manual operation that is inappropriate for selection is restricted based on detection by a circumstance sensor which detects the circumstances of use. For example, when the circumstance sensor detects acceleration, an operation to select an image-enlarging mode is restricted. This helps avoid an accident or the like. In this configuration, the user may be notified that the manual operation is inappropriate. According to another feature, a processing mode of the memory is selected automatically based on detection by the circumstance sensor. This makes it possible to automatically select a processing mode that suits the circumstances of use. 
         [0173]    According to a specific feature of the examples disclosed herein, the memory learns and stores a processing mode that suits the circumstances based on detection by the circumstance sensor at the time that a manual operation is done. This makes it possible to automatically select a processing mode of the memory based on what has been learned and stored and the corresponding detection by the circumstance sensor. Moreover, when a processing mode of the memory is selected automatically based on detection by the circumstance sensor, it is possible to judge based on what has been learned and stored whether the automatic selection is appropriate or not. 
         [0174]    According to another aspect of the examples disclosed herein, a vision aid system is provided that includes: an imager which images a target that a user intends to see; an image processor which corrects an image obtained by the imager to suit the user&#39;s vision disorder; a display which displays the image from the image processor so that the user sees it; and a controller which reduces the frame rate of image display on the display when the image processor enlarges an image. This helps alleviate motion sickness or the like visually induced when an image is enlarged. 
         [0175]    According to another aspect of the examples disclosed herein, a vision aid system is provided that includes: an imager which images a target that a user intends to see; an image processor which corrects an image obtained by the imager to suit the user&#39;s vision disorder; a display which displays the image from the image processor so that the user sees it; a circumstance sensor which detects the circumstances of use; and a controller which stops the display from changing display when the circumstance sensor detects minute vibrations. This helps alleviate motion sickness or the like visually induced by minute vibrations of an image. 
         [0176]    According to another aspect of the examples disclosed herein, a vision aid system is provided that includes: an imager which images a target that a user intends to see; an image processor which corrects an image obtained by the imager to suit the user&#39;s vision disorder; a display which displays the image from the image processor so that the user sees it; a circumstance sensor which detects the circumstances of use; and a controller which changes the processing by the image processor based on detection by the circumstance sensor. This makes it possible to change display automatically according to the circumstances. 
         [0177]    According to another aspect of the examples disclosed herein, a vision aid system is provided that includes: an imager which images a target that a user intends to see; an image processor which corrects an image obtained by the imager to suit the user&#39;s vision disorder; a display which displays the image from the image processor so that the user sees it; a circumstance sensor which detects the circumstances of use; a changer which changes the processing by the image processor; and a controller which effects an automatic return of the processing by the image processor to a standard state based on detection by the circumstance sensor. This makes it possible to automatically return from an image enlarging state for reading purposes to a real-scale state or a wide state for those with visual field constriction when, for example, the circumstance sensor detects acceleration resulting from the user starting to walk. 
         [0178]    According to yet another aspect of the examples disclosed herein, a binocular display is provided that includes a binocular display system which receives image information from a binocular imaging system having mutually parallel optical axes and which has an optical axis interval equivalent to the optical axis interval of the binocular imaging system. 
         [0179]    According to a specific feature, the binocular display provides a display virtual image at a distance equivalent to the standard subject distance of the binocular imaging system. 
         [0180]    According to another specific feature, the binocular display has a dioptric power adjusting function. 
         [0181]    According to another specific feature, the binocular display has an image enlarging function and an image reducing function. 
         [0182]    According to another aspect of the examples disclosed herein, a binocular display is provided that includes: a binocular display system which receives image information from a binocular imaging system having mutually parallel optical axes and which has an optical axis interval different from the optical axis interval of the binocular imaging system; and an image shifting function based on a difference between the optical axis interval of the binocular imaging system and the optical axis interval of the binocular display system. 
         [0183]    According to another aspect of the examples disclosed herein, a binocular display is provided that includes: a binocular display system having an optical axis interval adjusting function; and an image shifting function based on optical axis interval adjustment in the binocular display system. 
         [0184]    According to another aspect of the examples disclosed herein, a binocular display is provided that includes: a binocular display system which receives image information from a binocular imaging system having mutually parallel optical axes and which has a display optical system different from the binocular imaging system; and an image shifting function based on a difference of the display optical system. 
       INDUSTRIAL APPLICABILITY 
       [0185]    The present invention finds application in vision aid systems and binocular display apparatuses. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
         
           
               22 ,  24 ,  26 ,  28  imager 
               50  image processor 
               12 ,  18 ,  14 ,  20  display 
               32 ,  26  light transmitter 
               54  controller for controlling light transmitters 
               16  controller for displacing optical axes 
               56  memory 
               22 ,  24 ,  26 ,  28  imager 
               50  image processor 
               12 ,  18 ,  14 ,  20  display 
               72  memory for storing processing modes 
               58 ,  74  selector 
               40 ,  44 ,  66 ,  70  circumstance sensor 
               74  controller for lowering a frame rate of image display 
               74  controller for stopping display from being changed 
               74  controller for changing processing by an image processor 
               74  controller for an automatic return of processing by an image processor to a standard state 
               24 ,  28 ,  134 ,  136  binocular imaging system 
               12   a,    14   a,    18   a,    20   a  binocular display system 
               80 ,  81  image shifting function