Abstract:
A display apparatus adapted to generate image data for controlling a first light modulation section adapted to project a first window, and image data for controlling a second light modulation section adapted to project a second window smaller than the first window and projected so as to overlap with the first window, includes: a first image conversion section adapted to convert a resolution of input image data in accordance a resolution of the first light modulation section to form the image data for controlling the first light modulation section; and a second image conversion section adapted to extract data included in a range corresponding to a resolution of the second light modulation section among the input image data to form the image data for controlling the second light modulation section.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to a display apparatus, in particular to a display apparatus for projecting a first window with a first light modulation section and projecting a second window smaller than the first window with a second light modulation section in an overlapping manner. 
         [0003]    2. Related Art 
         [0004]    Since the past, in work using CAD, simulations, and so on, there have been a lot of cases in which details of a partial image of a display image such as a design drawing is confirmed while confirming the overall picture thereof, and in the case in which a display with a general purpose pixel count such as XGA is used, it is required to repeat zooming in and zooming out of the display image, which incurs decrease in work efficiency. Further, in the case in which the image is zoomed in for confirming the details of the partial image, the overall picture of the image becomes invisible, and therefore, it is difficult to grasp the positional relationship of the partial image with the overall picture. 
         [0005]    To cope with such a problem, it is desirable to use a high-resolution display capable of displaying an image pixel by pixel in accordance with a high pixel count image signal to be input thereto. Further, in order for confirming a detailed image, it is desirable that the pixel itself has a size of a visible level, and in that sense, projectors having a somewhat large display screen are one of the most suitable display apparatuses. However, in order for performing display based directly on the image signal with high pixel count, a projector provided with a light valve (e.g., a liquid crystal light valve) corresponding to the input image signal is required, which leads to incurring increase in apparatus cost. 
         [0006]    On the other hand, in a display with a large screen, it is natural for the user to view the screen from a position distant from the display to some extent when viewing the overall picture, and from a position close to the display because of limitation in resolution of the eyesight when viewing details thereof. 
         [0007]    Therefore, JP-A-2004-70257 (Document 1) discloses a projector capable of projecting a window representing partially detailed information in a screen displaying an overall picture in an overlapping manner, thereby confirming partial details without using a high-resolution display. Further, JP-A-2000-276123 (Document 2) and JP-A-2007-65542 (Document 3) disclose a technology of varying the display resolution in accordance with the observation distance of the user to the screen. For example, the technology of the Document 2 is for detecting the distance between the observer and the screen by a remote controller, and expanding the display image in the case in which the distance is large while shrinking the display image in the case in which the distance is small, thereby keeping the apparent resolution constant. The technology of the Document 3 is for controlling a zoom lens in accordance with the observation distance, thereby always displaying the overall information of the screen with the highest observable resolution for the observer. 
         [0008]    In the Document 1 described above, details of the control of the size and the position of the display made by a local projection projector adapted to perform display of a partial detailed image, for example, are not at all disclosed, and therefore, the disclosure thereof is insufficient for coping with the problem described above. Further, in either one of the Document 2 and the Document 3, since the size of the object varies in accordance with the observation distance, the size of the object thus displayed as described above does not vary, which is not suitable for the natural action of viewing the screen from a position closer thereto for confirming the details. Further, the action thereof is adverse to the action of getting closer for viewing the details in such away that the object displayed thereon becomes larger as the observation distance increases and smaller as it decreases, which is not suitable for CAD, simulations, and so on. 
       SUMMARY 
       [0009]    An advantage of some aspects of the invention is to provide a display apparatus capable of achieving the function equivalent to a high-resolution display with a relatively low cost, and of performing the display corresponding to the natural human action of getting away from the screen for viewing the overall picture while getting closer to the screen for viewing the details. 
         [0010]    According to an aspect of the invention, there is provided a display apparatus adapted to project, on a first window projected by a first light modulation section, a second window smaller than the first window by a second light modulation section in an overlapping manner, and including a first image conversion section adapted to convert a resolution of input image data in accordance a resolution of the first light modulation section to form the image data for controlling the first light modulation section, a second image conversion section adapted to extract data included in a range corresponding to a resolution of the second light modulation section among the input image data to form the image data for controlling the second light modulation section. 
         [0011]    According to the display apparatus having such a feature as described above, it is possible to display the second window with a higher resolution (the resolution of the input image data), while displaying the first window with a lower resolution (the resolution of the first light modulation section). In other words, in the work operation using CAD or a simulation, since there are a lot of cases in which it is enough to display partial detailed information in the second window with a higher resolution while displaying the overall picture in the first window with a lower resolution, it is possible to realize a desired characteristic at relatively low coast compared to the case of displaying the overall picture with a high resolution as in the related art. Further, since the observer gets away from the screen in the case of attempting to observe the whole at a time, it is not required to make the details visible in view of human eyesight, and further, since the observer gets closer to the screen in the case of observing the details, the range, which can be viewed in human eyesight at a time, becomes limited, and therefore, it is enough to make it possible to perform detailed display (high-resolution display) in part. 
         [0012]    Further, according to another aspect of the invention, there is provide a display apparatus adapted to project, on a first window projected by a first light modulation section, a second window smaller than the first window by a second light modulation section in an overlapping manner, and includes a first image conversion section adapted to convert a resolution of input image data in accordance a resolution of the first light modulation section to form the image data for controlling the first light modulation section, a window size parameter generation section adapted to generate a window size parameter for designating a size of the second window, a zoom ratio setting section adapted to set a zoom ratio of a projection lens disposed on a posterior stage of the second light modulation section based on the window size parameter, an extraction range setting section adapted to set an extraction range parameter for designating a range of data to be extracted among the input image data based on the window size parameter, a second image conversion section adapted to extract data included in an extraction range designated by the extraction range parameter from the input image data, and to convert a resolution of the extracted data according to needs from a relationship between the extraction range and a resolution of the second light modulation section, thereby forming the image data for controlling the second light modulation section, and a zoom control section adapted to control a zoom action of the projection lens in accordance with the zoom ratio set by the zoom ratio setting section. 
         [0013]    According to the display apparatus having such a feature as described above, the size of the second window can arbitrarily controlled using the value of the window size parameter, and the resolution of the second window can automatically be controlled in accordance with the size thereof. In other words, by reducing the second window by the window size parameter in the case in which the observer is located near the screen, and enlarging the second window when the observer is located away from the screen, it is possible to perform display corresponding to the natural human action of getting away from the screen for viewing the overall picture and getting closer to the screen for viewing the details. 
         [0014]    Further, in the display apparatus described above, it is preferable that the window size parameter generation section sets the window size parameter so that a size of an image displayed in the second window becomes constant irrespective of the size of the second window. 
         [0015]    Thus, it is possible in the case of varying the size of the second window to prevent the difference in size between the images displayed in the first window and the second window from occurring, thus it becomes possible to perform display without providing uncomfortable feeling to the observer. 
         [0016]    Further, in the display apparatus described above, it is preferable that an observation distance measurement section adapted to measure an observation distance from a projection screen of the first and second windows to an observer is further provided, and the window size parameter generation section generates the window size parameter based on a measurement result of the observation distance by the observation distance measurement section. 
         [0017]    Thus, it is possible to automatically control the size of the second window in accordance with the observation distance of the observer to the screen. In other words, by automatically reducing the second window when the observer is located at a position near the screen, and by automatically enlarging the second window when the observer is located at a position away from the screen, it is possible to perform display corresponding to the natural human behavior. 
         [0018]    Further, in the display apparatus described above, it is preferable that there are further provided an image quality setting section adapted to set an image quality control parameter for controlling image quality of the second window based on the window size parameter, and an image quality control section adapted to execute an image quality control process on the image data for controlling the second light modulation section obtained from the second resolution conversion section in accordance with the image quality control parameter. 
         [0019]    More specifically, it is preferable to set an image quality control parameter for controlling the brightness of the second window. 
         [0020]    Thus, it becomes possible to automatically control the image quality of the second window in accordance with the size of the second window. In particular, by automatically controlling the brightness, which is a significant factor for determining the image quality, improvement of the image quality of the second window can be achieved. 
         [0021]    Further, according to still another aspect of the invention, there is provided a display apparatus adapted to project, on a first window projected by a first light modulation section, a second window smaller than the first window by a second light modulation section in an overlapping manner, and includes a first image conversion section adapted to convert a resolution of input image data in accordance a resolution of the first light modulation section to form the image data for controlling the first light modulation section, a display position parameter generation section adapted to generate a display position parameter for designating a display position of the second window, an extraction range setting section adapted to set an extraction range parameter for designating a range of data to be extracted among the input image data, a second image conversion section adapted to move a position of the extraction range designated by the extraction range parameter based on the display position parameter, and to extract data included in the extraction range having been moved among the input image data to form the image data for controlling the second light modulation section, and a display position control section adapted to control the display position of the second window based on the display position parameter. 
         [0022]    According to the display apparatus having such a feature as described above, since the display position of the second window can arbitrarily controlled in accordance with the value of the display position parameter, the observer can freely display the desired verification section in the second window with a higher resolution, improvement in work efficiency can be achieved. 
         [0023]    Further, in the display apparatus described above, it is preferable that an observation location detection section adapted to detect an observation location of an observer in a plane parallel to the projection screen of the first and second windows is further provided, and the display position parameter generation section generates the display position parameter based on an observation location detection result by the observation location detection section. 
         [0024]    Thus, it is possible to automatically control the display position of the second window in accordance with the observation position of the observer to the screen, which making a contribution to improvement in work efficiency. 
         [0025]    Further, in the display apparatus described above, it is preferable that a window size parameter generation section adapted to generate a window size parameter for designating a size of the second window, a zoom ratio setting section adapted to set a zoom ratio of a projection lens disposed on a posterior stage of the second light modulation section based on the window size parameter, and a zoom control section adapted to control a zoom action of the projection lens in accordance with the zoom ratio set by the zoom ratio setting section are further provided, and the extraction range setting section sets the extraction range parameter based on the window size parameter, and the second image conversion section converts a resolution of the extracted data according to needs from a relationship between the extraction range designated by the extraction range parameter and the resolution of the second light modulation section, thereby forming the image data for controlling the second light modulation section. 
         [0026]    Thus, the display position of the second window can arbitrarily be controlled, and further, the size of the second window can also be controlled arbitrarily by the value of the window size parameter, and the resolution of the second window can automatically be controlled in accordance with the size thereof. 
         [0027]    Further, according to still another aspect of the invention, there is provided a display apparatus adapted to project, on a first window projected by a first light modulation section, a second window smaller than the first window by a second light modulation section in an overlapping manner, and includes a first image conversion section adapted to convert a resolution of input image data in accordance a resolution of the first light modulation section to form the image data for controlling the first light modulation section, a content analysis section adapted to analyze a characteristic of a content of the input image data, an observation information determination section adapted to determine an observation location of an observer based on an analytical result of the characteristic of the content by the content analysis section, a display position parameter generation section for generating the display position parameter for designating the display position of the second window based on the observation location determined by the observation information determination section, an extraction range setting section adapted to set an extraction range parameter for designating a range of data to be extracted among the input image data, a second image conversion section adapted to move a position of the extraction range designated by the extraction range parameter based on the display position parameter, and to extract data included in the extraction range having been moved among the input image data to form the image data for controlling the second light modulation section, and a display position control section adapted to control the display position of the second window based on the display position parameter. 
         [0028]    According to the display apparatus having such a feature as described above, it becomes possible to automatically control the display position of the second window in accordance with the characteristic of the content of the input image data. 
         [0029]    Further, in the display apparatus described above, it is preferable that the observation information determination section determines an observation distance in addition to the observation location of an observer based on the analytical result of the characteristic of the content, the display apparatus further includes a window size parameter generation section adapted to generate a window size parameter for designating the size of the second window based on the observation distance determined by the observation information determination section, a zoom ratio setting section adapted to set a zoom ratio of a projection lens disposed on a posterior stage of the second light modulation section based on the window size parameter, and a zoom control section adapted to control a zoom action of the projection lens in accordance with the zoom ratio set by the zoom ratio setting section, and the extraction range setting section sets the extraction range parameter based on the window size parameter, and the second image conversion section converts a resolution of the extracted data according to needs from a relationship between the extraction range designated by the extraction range parameter and the resolution of the second light modulation section, thereby forming the image data for controlling the second light modulation section. 
         [0030]    According to the above, the display position of the second window can automatically be controlled in accordance with the characteristic of the content of the input image data, and in addition, the size of the second window can also be controlled arbitrarily, and the resolution of the second window can automatically be controlled in accordance with the size thereof. 
         [0031]    Further, in the display apparatus described above, it is preferable that a blanking control section adapted to perform control so as to inhibit projection of projection light by the first light modulation section in an area where the first window and the second window overlap with each other. 
         [0032]    According to this aspect, even in the case in which the display positional relationship between the first window and the second window is slightly varied, there is no chance that the second window displaying important information overlaps the first window in the periphery thereof, thus degradation in the resolution of the projection image can be prevented. 
         [0033]    Further, in the display apparatus described above, it is preferable that the first light modulation section and the second light modulation section have the same resolution. 
         [0034]    According to the above, since the light modulation section with the same resolution can be used, the same model can commonly be used therein, and further, since it is enough to prepare a single unit of the same model as maintenance equipment, it is possible to achieve reduction of maintenance cost. 
         [0035]    Further, in the display apparatus described above, it is preferable that the resolution of the first light modulation section and the second light modulation section is lower than the resolution of the input image data. 
         [0036]    Thus, the advantage of realizing the same function as the high-resolution display at relatively low cost becomes prominent. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]    The invention will now be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
           [0038]      FIG. 1  is a schematic diagram of a configuration of a display apparatus  1  according to a first embodiment of the invention. 
           [0039]      FIG. 2  is an internal configuration diagram of a first projector  18  in the display apparatus  1 . 
           [0040]      FIG. 3  is a detailed configuration diagram of an optical system  25  in the display apparatus  1 . 
           [0041]      FIG. 4  is a diagram showing projection windows W 1  and W 2  displayed on a screen SC by the display apparatus  1 . 
           [0042]      FIGS. 5A and 5B  are first explanatory diagrams related to an operation of the display apparatus  1 . 
           [0043]      FIGS. 6A and 6B  are second explanatory diagrams related to an operation of the display apparatus  1 . 
           [0044]      FIG. 7  is a diagram showing the projection windows W 1  and W 2  displayed on the screen SC by the display apparatus  1 . 
           [0045]      FIG. 8  is a schematic diagram of a configuration of a display apparatus  2  according to a second embodiment of the invention. 
           [0046]      FIG. 9  is an internal configuration diagram of a parameter generation section  33  in the display apparatus  2 . 
           [0047]      FIGS. 10A through 10D  are explanatory diagrams related to the respective parameters of the parameter generation section  33  in the display apparatus  2 . 
           [0048]      FIG. 11  is a first explanatory diagram related to an operation of the display apparatus  2 . 
           [0049]      FIGS. 12A and 12B  are second explanatory diagrams related to an operation of the display apparatus  2 . 
           [0050]      FIG. 13  is a schematic diagram of a configuration of a display apparatus  3  according to a third embodiment of the invention. 
           [0051]      FIGS. 14A and 14B  are internal configuration diagrams of an observation location detection section  40  in the display apparatus  3 . 
           [0052]      FIG. 15  is a detailed configuration diagram of an optical system  25  in the display apparatus  3 . 
           [0053]      FIG. 16  is a diagram showing the projection windows W 1  and W 2  displayed on the screen SC by the display apparatus  3 . 
           [0054]      FIG. 17  is a schematic diagram of a configuration of a display apparatus  4  according to a fourth embodiment of the invention. 
           [0055]      FIGS. 18A and 18B  are internal configuration diagrams of an content analysis section  50  in the display apparatus  4 . 
           [0056]      FIG. 19  is an explanatory diagram of an operation of the display apparatus  4 . 
           [0057]      FIGS. 20A and 20B  are explanatory diagrams related to a modified example of the present embodiment. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0058]    Hereinafter, an embodiment of a display apparatus according to the invention will be explained with reference to the accompanying drawings. 
       First Embodiment 
       [0059]    Firstly, a display apparatus according to a first embodiment of the invention will be explained.  FIG. 1  is a schematic diagram of a configuration of the display apparatus  1  according to the first embodiment. As shown in  FIG. 1 , the present display apparatus  1  is composed of an A/D converter  10 , an image memory  11 , a first resolution conversion circuit  12 , a second resolution conversion circuit  13 , a first image buffer  14 , a second image buffer  15 , a first output circuit  16 , a second output circuit  17 , a first projector  18 , and a second projector  19 . 
         [0060]    The display apparatus  1  thus configured is for projecting an image corresponding to the image signal input from a computer PC to display it on a screen SC. The computer PC is capable of processing the image signal, for example, of a personal computer or a DVD player. Further, the screen SC can be either one of a front screen observed from a projection side and a rear screen observed from an opposite side to the projection side. 
         [0061]    The A/D converter  10  converts the image signal input from the computer PC into digital data, and outputs image data thus obtained to the image memory  11 . Here, in the present embodiment, there is assumed a signal of QXGA (2048×1536), which has a resolution (pixel count) two times as high (large) as XGA (1024×768) in both of horizontal and vertical directions, as the image signal transmitted from the computer PC. Further, although the image signal output from the computer PC is generally composed of signals corresponding respectively to three colors of R (red), G (green), and B (blue), since the three lines are output in parallel to each other in reality, and the processes in the display apparatus  1  are also executed simultaneously, the explanations will hereinafter be presented focusing attention on a signal of one of the three lines as a representative. 
         [0062]    It should be noted that in the case in which the output of the computer PC is digital data, it is not required to provide the A/D converter  10 , and it is enough to directly connect the image memory  11  and the computer PC to each other. Further, a dot clock signal, a timing signal, and so on necessary for operation of the A/D converter  10  and writing of the image data in the image memory  11  are generated by a timing circuit not shown such as a PLL circuit based on a sync signal included in the image signal. 
         [0063]    The image memory  11  divides the image data input from the A/D converter  10  into data each corresponding to one pixel, and stores the data in a memory area to which addresses “0” through “2047” in the X direction and addresses “0” through “1535” in the Y direction are assigned. Further, the image memory  11  outputs the image data stored therein to the first resolution conversion circuit  12  and the second resolution conversion circuit  13  at predetermined timing. It should be noted that the image memory  11  is required to have a capacity enough to store the image data (the data corresponding to the pixel count of 2048×1536) corresponding to at least one frame. 
         [0064]    The first resolution conversion circuit (a first image conversion section)  12  converts the resolution of the image data input from the image memory  11  so as to correspond to the resolution of a liquid crystal light valve (see a first light modulation section in  FIG. 3 ) provided to the first projector  18 . As described later, since it is assumed that the resolution of the liquid crystal light valve used in the present embodiment is XGA, the first resolution conversion circuit  12  converts the resolution (QXGA) of the image data input from the image memory  11  into XGA, and outputs the image data with the converted resolution to the first image buffer  14 . 
         [0065]    The second resolution conversion circuit (a second image conversion section)  13  extracts the image data included in a size (range) corresponding to the resolution of a liquid crystal light valve (a second light modulation section) provided to the second projector  19  among the image data input from the image memory  11 . As described later, since it is assumed that the resolution of the liquid crystal light valve used in the present embodiment is XGA, the second resolution conversion circuit  13  extracts the data included in the size (i.e., a half size) corresponding to XGA among the image data (QXGA). More specifically, the second resolution conversion circuit  13  extracts the image data included in the range corresponding to the X address of “511” through “1535” and the Y address of “383” through “1151” among the image data, and outputs it to the second image buffer  15 . 
         [0066]    The first image buffer  14  buffers the image data (the image data converted to XGA) input from the first resolution conversion circuit  12 , and outputs the image data, which is stored therein, to the first output circuit  16  at predetermined timing. Further, the first image buffer  14  has a function of converting the image data at a predetermined address into black data and then outputting it in response to a blanking signal input from the second image buffer  15 . 
         [0067]    The second image buffer (a blanking control section)  15  buffers the image data (the image data corresponding to an XGA size) input from the second resolution conversion circuit  13 , and outputs the image data, which is stored therein, to the second output circuit  17  at predetermined timing. Further, the second image buffer  15  outputs a blanking signal, which is used for converting the image data at a predetermined address among the image data output from the first image buffer  14  into black data, to the first image buffer  14 . Although described later in detail, the blanking signal is for preventing the projection image by the first projector  18  and the projection image by the second projector  19  from overlapping with each other. 
         [0068]    The first output circuit  16  outputs the image data input from the first image buffer  14  to the first projector  18 . The second output circuit  17  outputs the image data input from the second image buffer  15  to the second projector  19 . 
         [0069]    The first projector  18  projects the image, which corresponds to the image data (the image data converted into XGA) input from the first output circuit  16 , on the screen SC. The second projector  19  projects the image, which corresponds to the image data (the image data corresponding to the XGA size) input from the second output circuit  17 , on the screen SC as a projection window with a size half as large as the projection window of the first projector  18 . Since the internal configurations of the first and second projectors  18 ,  19  are the same, the internal configuration will hereinafter be explained using the first projector  18  as a representative. 
         [0070]      FIG. 2  is a block diagram representing the internal configuration of the first projector  18 . As shown in  FIG. 2 , the first projector  18  is composed of an interface circuit  20 , a scaling circuit  21 , an image quality control circuit (an image quality control section)  22 , a gamma adjustment circuit  23 , a drive circuit  24 , and an optical system  25 . It should be noted that although it is composed of three systems of R, G, and B in reality, since all of the systems have the same configuration, the explanations will be presented illustrating only one of the systems in  FIG. 2 . 
         [0071]    The interface circuit  20  assumes communication of the data between the first projector  18  and the output circuit  16 , and outputs the image data input from the first output circuit  16  (the second output circuit  17  in the case with the second projector  19 ) to the scaling circuit  21 . 
         [0072]    The scaling circuit  21  has a function of converting the resolution of the image data input from the interface circuit  20  so as to correspond to the resolution of the liquid crystal light valve provided to the optical system  25 , and a keystone distortion correction function for electrically correcting the keystone distortion caused by a mechanical factor of the optical system  25 . The scaling circuit  21  outputs the image data, on which the resolution conversion and the keystone distortion correction described above have been executed, to the image quality control circuit  22 . It should be noted that in the present embodiment, since it is assumed that the resolution of the liquid crystal light valve used therein is XGA, the resolution conversion is not executed in the scaling circuit  21 . 
         [0073]    The image quality control circuit  22  has a function of controlling the image quality such as brightness or contrast, and executes a brightness control process, a contrast control process, and so on on the image data input from the scaling circuit  21 , and then outputs the image data, on which the image control has been executed, to the gamma adjustment circuit  23 . The gamma adjustment circuit  23  executes gamma adjustment, which corresponds to an input signal-to-light modulation characteristic of the liquid crystal light valve, on the image data input from the image quality control circuit  22 , and then outputs the image data, on which the gamma adjustment has been executed, to the drive circuit  24 . The drive circuit  24  generates a drive signal for driving the liquid crystal light valve provided to the optical system  25 , base on the image data input from the gamma adjustment circuit  23 , and then outputs the drive signal to the liquid crystal light valve. 
         [0074]      FIG. 3  is a detailed configuration diagram of the optical system  25 . As shown in  FIG. 3 , the optical system  25  is composed of an illumination optical system  100 , a color separation optical system  110 , a relay optical system  120 , a red liquid crystal light valve  130 R, a green liquid crystal light valve  130 G, a blue liquid crystal light valve  130 B, a cross dichroic prism  140 , and a projection optical system  150 . 
         [0075]    The illumination optical system  100  is composed of a light source  101  and a polarization conversion element  102 . The light source  101  is, for example, a super high-pressure mercury lamp, and emits white light including light spectrums of R, G, and B. The polarization conversion element  102  converts (polarizes) the polarization direction of the white light emitted from the light source  101  into a constant direction, and emits it to the color separation optical system  110 . 
         [0076]    The color separation optical system  110  is composed of dichroic mirrors  111 ,  112  and a reflecting mirror  113 . The dichroic mirror  111  transmits the red light L R  among the white light input from the illumination optical system  100 , to the reflecting mirror  113 , and at the same time, reflects the blue light and the green light toward the dichroic mirror  112 . The reflecting mirror  113  reflects the red light input from the dichroic mirror  111  toward the red liquid crystal light valve  130 R. On the other hand, the dichroic mirror  112  reflects the green light L G  among the blue light and the green light input from the dichroic mirror  111 , toward the green liquid crystal light valve  130 G, and at the same time, transmits the blue light L B  to the relay optical system  120 . 
         [0077]    The relay optical system  120  is composed of relay lenses  121 ,  122 ,  123 , and reflecting mirrors  124 ,  125 . The blue light L B  separated by the color separation optical system  110  is emitted toward the blue liquid crystal light valve  130 B via the relay lens  121 → the reflecting mirror  124 → the relay lens  122 → the reflecting mirror  125 → the relay lens  123  in this order. 
         [0078]    The red liquid crystal light valve  130 R, the green liquid crystal light valve  130 G, and the blue liquid crystal light valve  130 B are driven by the drive signals supplied from the drive circuits  24  corresponding respectively thereto, modulate (execute intensity control on) the colored light (red light, green light, and blue light) input respectively thereto, and then output it to the cross dichroic prism  140 . The cross dichroic prism  140  is obtained by bonding four rectangular prisms to each other with a dielectric multilayer film for reflecting the red light and a dielectric multilayer film for reflecting the blue light formed on the inner surface of the rectangular prisms so as to form a cross shape, and the three colored light beams are combined by the dielectric multilayer films, and emitted to the projection optical system  150  as light beams expressing a color image. 
         [0079]    The projection optical system  150  is composed of a projection lens  151 , an electric focus  152 , and an electric zoom  153 . The projection lens  151  enlargedly projects the combined light beam input from the cross dichroic prism  140  on the screen SC in accordance with the magnifying power (zoom ratio) controlled by the electric zoom  153 . The electric focus  152  performs focus control of the projection lens  151  automatically or by a manual operation. The electric zoom (zoom control section)  153  controls the magnifying power of the size of the projection window by the projection lens  151  automatically or by a manual operation. 
         [0080]    Here, mounting positions, zoom ratio, and focus of the respective projectors are controlled so that, with respect to the projection window W 1  (a first window) of the first projector  18 , the projection window W 2  (a second window) of the second projector  19  is projected at the center of the projection window W 1  and with a size half as large as the size of the projection window W 1  in both of the horizontal and the vertical directions as shown in  FIG. 4 . 
         [0081]    An operation of the display apparatus  1  having the configuration described above will hereinafter be explained. 
         [0082]    Firstly, the image signal input from the computer PC is converted into an image data by the A/D converter  10 , and then written into the image memory  11  frame by frame.  FIG. 5A  shows the image data written in the image memory  11 . As shown in  FIG. 5A , the image data is divided into data each corresponding to one pixel, and stored in a memory area to which addresses “0” through “2047” in the X direction and addresses “0” through “1535” in the Y direction are assigned. It should be noted that “am, n” denotes the image data stored at the address (X, Y)=(m, n). 
         [0083]    The image data thus stored in the image memory  11  is output to the first resolution conversion circuit  12  and the second resolution conversion circuit  13  frame by frame at predetermined timing. Then, the first resolution conversion circuit  12  converts the resolution (QXGA) of the image data input from the image memory  11  into XGA. Specifically, the first resolution conversion circuit  12  calculates an average value of the image data in every block of four pixels adjacent to each other as shown in  FIG. 5A , thereby converting the blocks into the image data “b0, 0” through “b1023, 767” corresponding respectively to the pixels in XGA as shown in  FIG. 5B . In other words, the image data “b0, 0” corresponding to the address (X, Y)=(0, 0) of XGA, for example, is calculated along the formula 1 described below. 
         [0000]      “ b 0,0”={“ a 0,0”+“ a 1,0”+“ a 0,1”+“ a 1,1”}/4  (1) 
         [0084]    The image data thus converted to have a resolution of XGA by the first resolution conversion circuit  12  is stored in the first image buffer  14 . Specifically, as shown in  FIG. 5B , the image data thus converted into XGA is divided into data each corresponding to one pixel, and stored in a memory area of the first image buffer  14  to which addresses “0” through “1023” in the X direction and addresses “0” through “767” in the Y direction are assigned. 
         [0085]    On the other hand, the second resolution conversion circuit  13  extracts the data in a range with a size (i.e., a half size) corresponding to XGA among the image data (QXGA) input from the image memory  11 . Specifically, the second resolution conversion circuit  13  extracts the image data included in the range corresponding to the X address of “511” through “1535” and the Y address of “383” through “1151” among the image data, as shown in  FIG. 6A . 
         [0086]    The image data thus extracted so as to have the size corresponding to XGA by the second resolution conversion circuit  13  is stored in the second image buffer  15 . As shown in  FIG. 6B , the image data thus extracted is divided into data each corresponding to one pixel, and stored in a memory area of the second image buffer  15  to which addresses “0” through “1023” in the X direction and addresses “0” through “767” in the Y direction are assigned. Specifically, here, only the address conversion is executed, and for example, the image data “a511, 383” is converted into the image data “c0, 0” corresponding to the address (X, Y)=(0, 0) of XGA, and the image data “a1535, 1151” is converted into the image data “c1023, 767” corresponding to the address (X, Y)=(1023, 767) of XGA. 
         [0087]    As described above, the image data (the image data converted into XGA) stored in the first image buffer  14  is output to the first projector  18 , and at the same time, the image data (the image data corresponding to the XGA size) stored in the second image buffer  15  is output to the second projector  19 . 
         [0088]    Thus, the first projector  18  projects the image corresponding to the image data converted into XGA on the screen SC, and at the same time, the second projector  19  projects the image corresponding to the image data equivalent to the XGA size on the screen SC.  FIG. 7  is a diagram showing an example of the windows displayed on the screen SC. As shown in  FIG. 7 , with respect to the projection window W 1  of the first projector  18 , the projection window W 2  of the second projector  19  is projected at the center thereof with a size half as large as the size of the projection window W 1  in both of the horizontal and the vertical directions. In other words, in accordance with the input image signal (with a resolution of QXGA), display is performed in the range (the projection window W 2 ) half as large as the screen in both of the vertical and lateral directions at the central section thereof directly with the resolution of the input image signal, while in the peripheral section (the projection window W 1 ), display is performed with a half resolution (XGA) in both of the horizontal and vertical directions. 
         [0089]    In general, since important information is often displayed near the center of the screen, it is often enough to display the central portion in detail (with a higher resolution) and display the peripheral portion roughly (with a lower resolution) as described above. As described above, according to the display apparatus  1  in the present first embodiment, it is possible to realize a desired characteristic at a relatively low cost compared to the case of displaying the whole with a high resolution as in the related art. In other words, since the observer gets away from the screen SC in the case of attempting to observe the whole at a time, it is not required to make the details visible in view of human eyesight, and further, since the observer gets closer to the screen SC in the case of observing the details, the range, which can be viewed in human eyesight at a time, becomes limited, and therefore, it is enough to make it possible to perform detailed display (high-resolution display) in part. 
         [0090]    Further, since there is adopted the configuration in which blanking (display with black data) is provided to a part of the peripheral coarse projection window W 1  corresponding to the high-resolution area at the center of the screen, there is no chance for the projection window W 2  displaying the important information and the peripheral projection window W 1  to overlap with each other even in the case in which, for example, the relative position between the first projector  18  and the second projector  19  is slightly shifted, thereby making it possible to prevent the degradation in the resolution of the projection image. 
         [0091]    Further, since the liquid crystal light valves with the same resolution (pixel count) can be used in the two projectors (the first projector  18  and the second projector  19 ), the same model can commonly be used therein, and further, since it is enough to prepare a single unit of the same model as maintenance equipment, it is possible to achieve reduction of maintenance cost. 
       Second Embodiment 
       [0092]    Then, a display apparatus according to a second embodiment of the invention will be explained. The second embodiment relates to a display apparatus capable of varying the size of the projection window W 2  by the second projector  19  in accordance with the distance from the screen SC to the observer. 
         [0093]      FIG. 8  is a schematic diagram of a configuration of the display apparatus  2  according to the second embodiment. It should be noted that in  FIG. 8 , substantially the same constituents as those shown in  FIG. 1  (the first embodiment) are denoted with the same reference numerals, and the explanations therefor will be omitted. As shown in  FIG. 8 , the display apparatus  2  in the second embodiment is additionally provided with an observation distance measurement section  30 , an observation distance manually setting section  31 , a switching circuit  32 , and a parameter generation section  33 . 
         [0094]    The observation distance measurement section  30  measures the distance d from the screen SC to the observer, and outputs an observation distance signal representing the measurement result to the switching circuit  32 . As the observation distance measurement section  30 , there can be used a distance measuring instrument known to the public, for example, for emitting an ultrasonic wave, an infrared ray, or the like toward the observer, and measuring the time until the emitted wave returns. The observation distance manually setting section  31  is for setting the observation distance by a manual operation, and outputs the observation distance signal corresponding to the setting value to the switching circuit  32 . 
         [0095]    The switching circuit  32  selects either one of the observation distance signals respectively input from the observation distance measurement section  30  and the observation distance manually setting section  31 , and outputs the observation distance signal thus selected to the parameter generation section  33 . It should be noted that although it is explained for the sake of convenience that the setting value of the observation distance manually setting section  31  is set to be the value corresponding to the observation distance, the value is not necessarily required to be faithful to the actual observation distance, but can arbitrarily be set while actually observing the display screen since the size of the projection window by the second projector  19  can be varied in the display apparatus  2  of the present second embodiment as described later. 
         [0096]    The parameter generating section  33  generates an extraction range designation signal for designating a range of the data to be extracted from the image data (with a resolution of QXGA) stored in the image memory  11 , a zoom signal for controlling the electric zoom  153  in the second projector  19 , and an image quality control signal for controlling the image quality control circuit  22  in the second projector  19 , based on the observation distance signal input from the switching circuit  32 . The extraction range designation signal is output to the second resolution conversion circuit  13 , the zoom signal is output to the electric zoom  153  in the second projector  19 , and the image quality control signal is output to the image quality control circuit  22  in the second projector  19 . 
         [0097]      FIG. 9  is a detailed configuration diagram of the parameter generation section  33 . As shown in  FIG. 9 , the parameter generation section  33  is composed of a window size parameter generation section  33   a , a zoom signal generation section  33   b , an image quality control signal generation section  33   c , and an extraction range generation section  33   d.    
         [0098]    As shown in  FIG. 10A , the window size parameter generation section  33   a  obtains a window size parameter SP corresponding to the observation distance d represented by the observation distance signal input from the switching circuit based on the correspondence between the observation distance d and the window size parameter SP, and outputs the window size parameter SP thus obtained to the zoom signal generation section  33   b , the image quality control signal generation section  33   c , and the extraction range generation section  33   d.    
         [0099]    Here, the window size parameter SP is data for designating the size (window size) of the projection window W 2  of the second projector  19 . Since the size of the projection window W 2  of the second projector  19  is determined in relation to the size of the projection window W 1  of the first projector  18 , the upper limit value SPmax of the window size parameter SP in  FIG. 10A  is set to be a value with which the size of the projection window W 2  becomes the same as the size of the projection window W 1  of the first projector  18 , and the lower limit value SPmin thereof on the other hand is set to be a value with which the size of the projection window W 2  becomes half as large as the size of the projection window W 1  of the first projector  18 . It should be noted that it is enough for these setting values to be determined in accordance with the image signal input from the computer PC, the relationship in resolution (pixel count) between the first projector  18  and the second projector  19 , and further, the zoom ratio of the projection lens  151  of the second projector  19 , and the setting values are not limited to the values described above. Further, although the value approximately proportional to the observation distance d is set between the upper limit value SPmax and the lower limit value SPmin, any simply increasing characteristic can actually be adopted. 
         [0100]    As shown in  FIG. 10B , the zoom signal generation section (zoom ratio setting section)  33   b  obtains the zoom ratio Zm corresponding to the window size parameter SP input from the window size parameter generation section  33   a  based on the correspondence between the zoom ration Zm and the window size parameter SP set previously, and generates the zoom signal corresponding to the zoom ratio Zm thus obtained to output it to the second projector  19 . Since the zoom signal is for controlling the electric zoom  153  of the second projector  19  (i.e., for controlling the size of the projection window W 2  of the second projector  19 ), the zoom ratio Zm is set to be proportional to the window size parameter SP or to monotonically increase between the upper limit value SPmax and the lower limit value SPmin of the window size parameter SP, as shown in  FIG. 10B . 
         [0101]    As shown in  FIG. 10C , the image quality control signal generation section (image quality setting section)  33   c  obtains the image quality control parameter LP corresponding to the window size parameter SP input from the window size parameter generation section  33   a  based on the correspondence between the image quality control parameter LP and the window size parameter SP set previously, and generates the image quality control signal corresponding to the image quality control parameter LP thus obtained to output it to the second projector  19 . It should be noted that in  FIG. 10C , a brightness control parameter for controlling the brightness of the image is assumed as the image quality control parameter LP, and the image quality control parameter LP is set to have a characteristic inversely proportional to the window size parameter SP between the upper limit value SPmax and the lower limit value SPmin thereof. 
         [0102]    Since the area of the window of the projector is proportional to the square of the size of the window, when reducing the size of the window while keeping the light output of the second projector  19  constant, the luminance of the window becomes higher in proportion to the square of the size of the window. For example, the luminance with a half size is four times as high as the original luminance. Therefore, by controlling the brightness with the characteristic as shown in  FIG. 10C , it is possible to set the brightness of the projection window W 2  of the second projector  19  to be approximately the same level as the brightness of the projection window W 1  of the first projector  18  regardless of the size of the projection window W 2 , thereby preventing uncomfortable feeling. It should be noted that it is possible to set the brightness of the projection window W 2  to be different from the brightness of the projection window W 1 , to set the level of the black area, and to vary an edge reinforcement characteristic in accordance with the selection and setting of the control object of the image quality, and it is enough to set them in accordance with the actual installation environment, the purpose of use, the preference of the observer, and so on. 
         [0103]    As shown in  FIG. 10D , the extraction range generation section (extraction range setting section)  33   d  obtains an extraction range parameter DP corresponding to the window size parameter SP input from the window size parameter generation section  33   a  based on the correspondence between the extraction range parameter DP and the window size parameter SP set previously, and generates the extraction range designation signal corresponding to the extraction range parameter DP thus obtained to output it to the second resolution conversion circuit  13 . 
         [0104]    As shown in  FIG. 10D , the extraction range parameter DP (extraction range designation signal) is for designating the range of the data to be extracted from the image data (with the resolution of QXGA) stored in the image memory  11  (in other words, for designating the range of the image data to be actually displayed in the projection window W 2  of the second projector  19 ), and therefore, is set so as to be proportional to the window size parameter SP or to monotonically increase between the upper limit value SPmax and the lower limit value SPmin of the window size parameter. Here, the extraction range parameter DP corresponding to the lower limit value SPmin of the window size parameter is set to be, for example, “0.5,” and the extraction range parameter DP corresponding to the upper limit SPmax is set to be “1.” 
         [0105]    On the other hand, the electric zoom  153  of the second projector  19  in the present second embodiment controls the zoom ratio Zm of the projection lens  151  based on the zoom signal input from the parameter generation section  33  (the zoom signal generation section  33   b ) described above. Further, the image quality control circuit  22  of the second projector  19  executes the image quality (brightness) control process on the image data input from the scaling circuit  21  based on the image quality control signal input from the parameter generation section  33  (the image quality control signal generation section  33   c ), and then outputs the image data on which the image quality control is executed to the gamma adjustment circuit  23 . Further, the second resolution conversion circuit  13  in the present second embodiment executes extraction of the data in the designated range among the image data (with the resolution of QXGA) input from the image memory  11  based on the extraction range designation signal input from the parameter generation section  33  (the extraction range generation section  33   d ), and the process of converting the resolution according to needs. 
         [0106]    An operation of the present display apparatus  2  having the configuration described above will hereinafter be explained. 
         [0107]    Firstly, the operation is the same as in the first embodiment in that the image signal input from the computer PC is converted by the A/D converter  10  into the image data, then written in the image memory  11  frame by frame, and output to the first resolution conversion circuit  12  and the second resolution conversion circuit  13  frame by frame at predetermined timing. In contrast, in the operation of the present display apparatus  2 , the observation distance measurement section  30  continuously measures the distance from the screen SC to the observer, and the observation distance signal representing the measurement result (observation distance d) is output to the switching circuit  32 . Here, it is assumed that the switching circuit  32  selects the observation distance signal of the observation distance measurement section  30 , and then outputs it to the parameter generation section  33 . 
         [0108]    The window size parameter generation section  33   a  in the parameter generation section  33  obtains the window size parameter SP corresponding to the observation distance d represented by the observation distance signal input from the switching circuit  32  based on the characteristic data shown in  FIG. 10A . For example, the shorter the observation distance d is (the closer to the screen SC the observer is located), the closer to the lower limit value SPmin the window size parameter SP gets, thus the window size parameter SP becomes to have a value with which the size of the projection window W 2  of the second projector  19  becomes smaller (half as large as the size of the projection window W 1  at a minimum). On the other hand, the longer the observation distance d is (the further to the screen SC the observer is located), the closer to the upper limit value SPmax the window size parameter SP gets, thus the window size parameter SP becomes to have a value with which the size of the projection window W 2  of the second projector  19  becomes larger (the same size as the size of the projection window W 1  at a maximum). 
         [0109]    Further, the zoom signal generation section  33   b  obtains the zoom ratio Zm corresponding to the window size parameter SP based on the characteristic data shown in  FIG. 10B , and generates the zoom signal corresponding to the zoom ratio Zm thus obtained to output it to the second projector  19 . For example, in the case in which the window size parameter SP takes the lower limit value SPmin, the zoom ratio Zm with which the size of the projection window W 2  of the second projector  19  is set to be half as large as the size of the projection window W 1  of the first projector  18  is obtained. Meanwhile, in the case in which the window size parameter SP takes the upper limit value SPmax, the zoom ratio Zm with which the size of the projection window W 2  of the second projector  19  is set to be the same as the size of the projection window W 1  of the first projector  18  is obtained. 
         [0110]    Further, the image quality control signal generation section  33   c  obtains the image quality control parameter LP corresponding to the window size parameter SP based on the characteristic data shown in  FIG. 10C , and generates the image quality control signal corresponding to the image quality control parameter LP thus obtained to output it to the second projector  19 . For example, in the case in which the window size parameter SP takes the lower limit value SPmin (the case in which the size of the projection window W 2  of the second projector  19  is the smallest), the image quality control parameter LP with which the brightness of the projection window W 2  of the second projector  19  is set to be the lowest is obtained. Meanwhile, in the case in which the window size parameter SP takes the upper limit value SPmax (the case in which the size of the projection window W 2  of the second projector  19  is the largest), the image quality control parameter LP with which the brightness of the projection window W 2  of the second projector  19  is set to be the highest is obtained. 
         [0111]    Further, the extraction range generation section  33   d  obtains the extraction range parameter DP corresponding to the window size parameter SP based on the characteristic data shown in  FIG. 10D , and generates the extraction range designation signal corresponding to the extraction range parameter DP thus obtained to output it to the second resolution conversion circuit  13 . In the case in which the window size parameter SP takes the lower limit value SPmin, for example, the extraction range parameter DP (“0.5”), with which the data extraction range is designated to be the size (XGA size) half as large as the size of the image data (with the resolution of QXGA) stored in the image memory  11 , is obtained similarly to the case of the first embodiment. Meanwhile, in the case in which the window size parameter SP takes the upper limit value SPmax, the extraction range parameter DP (“1”), with which the range of the data to be extracted from the image data (with the resolution of QXGA) stored in the image memory  11  is designated to be the overall range thereof, is obtained. 
         [0112]    Meanwhile, the first resolution conversion circuit  12  converts the resolution (QXGA) of the image data input from the image memory  11  into XGA, and the image data thus converted is stored in the first image buffer  14 . Such operations are the same as in the first embodiment, and therefore, detailed explanations therefor will be omitted. 
         [0113]    On the other hand, the second resolution conversion circuit  13  extracts the data included in the extraction range thus designated among the image data (QXGA) input from the image memory  11  based on the extraction range designation signal input from the parameter generation section  33  (the extraction range generation section  33   d ). Specifically, in the case with the extraction range designation signal representing the extraction range parameter DP=“0.5,” the second resolution conversion circuit  13  extracts the data in a range with a size (i.e., a half size) corresponding to XGA among the image data (QXGA) input from the image memory  11 , similarly to the case of the first embodiment. Further, in the case with the extraction range designation signal representing the extraction range parameter DP=“1,” the second resolution conversion circuit  13  executes the same process as the resolution conversion process by the first resolution conversion circuit  12  (specifically, the resolution (QXGA) of the image data input from the image memory  11  is converted into XGA). 
         [0114]    Here, an operation of the second resolution conversion circuit  13  in the case in which the extraction range parameter DP takes a value between “1” and “0.5” will be explained with reference to the flowchart shown in  FIG. 11 . It should be noted that the explanations will hereinafter presented assuming the operation with the extraction range parameter DP of “0.75,” namely, the operation of extracting the data included in the range with a size corresponding to ¾ at the center thereof among the image data (QXGA) input from the image memory  11 , and then converting it to have a resolution of XGA. 
         [0115]    As shown in  FIG. 11 , the second resolution conversion circuit  13  firstly reads the extraction range parameter DP (“0.75” here) from the extraction range designation signal input therein (step S 1 ). Then, the second resolution conversion circuit  13  determines the number of data to be extracted from the image memory  103  in each of the X address direction and the Y address direction (step S 2 ). Here, since the extraction range parameter DP=“0.75” is assumed, the number of data in the X address direction becomes 2048×0.75=1536, and the number of data in the Y address direction becomes 1536×0.75=1153. 
         [0116]    Subsequently, the second resolution conversion circuit  13  determines the read starting address and the read ending address of the extraction data (step S 3 ). Specifically, taking the fact that the center of the extraction range is identical to the center of the overall range of the image and the address starts from “0” into consideration, the read starting and ending addresses in the X direction and the read starting and ending addresses in the Y direction are obtained as follows. 
         [0117]    Read starting address in the X direction: (2048−1536)/2=256 
         [0118]    Read ending address in the X direction: 256+1536−1=1792 
         [0119]    Read starting address in the Y direction: (1536−1153)/2=191.5→192 
         [0120]    Read ending address in the Y direction: 192+1153−1=1344 
         [0121]    Then, the second resolution conversion circuit  13  extracts the data included in the extraction range indicated by the read starting and ending addresses in the X direction and the read starting and ending addresses in the Y direction thus determined as described above, and converts the image data, thus extracted, to have a resolution of XGA using an interpolation calculation (step S 4 ). The resolution conversion process will be explained with reference to  FIGS. 12A and 12B .  FIG. 12A  shows the data “a256, 192” through “a1792, 1344” included in the extraction range indicated by the addresses described above. 
         [0122]    Here, in order for converting the number of data  1536  in the X address direction into the number of data  1024  of XGA, it is enough to execute the conversion of multiplication by ⅔ (the same can be applied to the Y direction). In other words, as shown in  FIG. 12A , it is enough to convert the data of each pixel into the data in the area corresponding to the thick frame D 1  by the interpolation calculation. Specifically, interpolation coefficients corresponding respectively to the four pixels adjacent to each other are set, and the interpolation coefficients are multiplied by the data of the respective pixels to calculate the average value, thereby obtaining the image data “d0, 0” through “d1023, 767” corresponding to the respective pixels of XGA. For example, the image data “d0, 0” corresponding to the address (X, Y)=(0, 0) can be calculated along the formula 2 described below. 
         [0000]      “ d 0,0”={“ a 256,192”·4+“ a 257,192”·2+“ a 256,193”·2+“ a 257,193”}/9  (2) 
         [0123]    The image data (the resolution conversion is executed in the case in which the extraction range parameter DP takes a value other than “0.5”) thus extracted and converted to have a resolution of XGA by the second resolution conversion circuit  13  is stored in the second image buffer  15 . Specifically, as shown in  FIG. 12B , the image data thus converted into XGA is divided into data each corresponding to one pixel, and stored in a memory area of the second image buffer  15  to which addresses “0” through “1023” in the X direction and addresses “0” through “767” in the Y direction are assigned. 
         [0124]    It should be noted that although the extraction range parameter DP can take any value between “0.5” and “1” in reality, a known method such as a bicubic method can be used as the interpolation calculation process besides the linear interpolation method in which the area of the pixel or the center of the pixel is taken as a representative point, and the interpolation coefficient corresponding to the distance between the pixels is set as described above. 
         [0125]    The image data stored in the first image buffer  14  as described above is output to the first projector  18 , and thus, the image corresponding to the image data converted into XGA is projected on the screen SC by the first projector  18 . This point is substantially the same as in the first embodiment. Meanwhile, the image data stored in the second image buffer  15  is output to the second projector  19 , and thus, the image corresponding to the image data converted into XGA is projected on the screen SC by the second projector  19 . On this occasion, the size and the brightness of the projection window W 2  thereof are controlled by the zoom signal and the image quality control signal generated in the parameter generation section  33 . 
         [0126]    For example, as described above, in the case in which the window size parameter SP takes the lower limit value SPmin, since the zoom ratio Zm with which the size of the projection window W 2  of the second projector  19  is set to be half as large as the size of the projection window W 1  of the first projector  18  is selected, on this occasion, the projection window W 2  is displayed with the size half as large as the size of the projection window W 1  by the control of the electric zoom  153  (similarly to the case of the first embodiment, see  FIG. 7 ). Further, in the case in which the window size parameter SP takes the lower limit value SPmin, since the image quality control parameter LP with which the brightness of the projection window W 2  of the second projector  19  becomes the lowest is selected, on this occasion, the brightness of the projection window W 2  is controlled to be the lowest by the image quality control process of the image quality control circuit  22 . 
         [0127]    Further, in the case in which the window size parameter SP takes the upper limit value SPmax, since the zoom ratio Zm with which the size of the projection window W 2  of the second projector  19  is set to be the same as the size of the projection window W 1  of the first projector  18  is selected, on this occasion, the projection window W 2  is displayed with the same size as the projection window W 1 . Further, in the case in which the window size parameter SP takes the upper limit value SPmax, since the image quality control parameter LP with which the brightness of the projection window W 2  of the second projector  19  becomes the highest is selected, on this occasion, the brightness of the projection window W 2  is controlled to be the highest. It should be noted that as described above, in the case in which the window size parameter SP takes the upper limit value SPmax, although it is assumed that the first projector  18  and the second projector  19  display substantially the same windows, since the projection window W 1  of the first projector  18  is set to be black by the blanking signal described in the first embodiment, degradation in image quality due to the overlap between the projection windows can be prevented. 
         [0128]    Obviously, in the case in which the window size parameter SP takes neither of the upper limit value SPmax and the lower limit value SPmin (e.g., the case in which the extraction range parameter DP takes “0.75” as described above), the projection window W 2  should be displayed with the size, the brightness, and the resolution corresponding to the window size parameter SP. 
         [0129]    As described above, according to the display apparatus  2  in the present second embodiment, since the size of the projection window W 2  of the second projector  19  can be varied in accordance with the observation distance d, and at the same time, the extraction range of the image data to be displayed in the projection window W 2  is varied in accordance with the observation distance d, it is possible to continue display without varying the size of the object displayed in the projection window W 2 . Therefore, it is possible to set the projection window W 2  to be smaller to display the image near the center thereof with the resolution of the input image signal in the case of making observation from a position close to the screen, and to display the image with the display resolution lowered in accordance the observation distance d so as to correspond to the resolution of the eyesight while keeping the apparent view angle approximately constant by enlarging the projection window W 2  in accordance with the distance in the case of making observation from a position away from the screen. Further, since the projection window W 1  of the first projector  18  is displayed constantly, it is possible to make observation from a position close to the screen if it is desired to view the details while constantly grasping the overall picture. 
       Third Embodiment 
       [0130]    Then, a display apparatus according to a third embodiment of the invention will be explained. In the first and the second embodiments described above, there is explained the case of displaying the projection window W 2  of the second projector  19  at the center of the projection window W 1  of the first projector  18 , namely the case in which the centers of the projection windows W 1 , W 2  are constantly the same. In contrast, the present third embodiment relates to a display apparatus capable of controlling the display position of the projection window W 2  in accordance with the location of the observer with respect to the inside of the surface of the screen SC. 
         [0131]      FIG. 13  is a schematic diagram of a configuration of the display apparatus  3  according to the third embodiment. It should be noted that in  FIG. 13 , substantially the same constituents as those shown in  FIG. 1  or  FIG. 8  are denoted with the same reference numerals, and the explanations therefor will be omitted. As shown in  FIG. 13 , the display apparatus  3  in the third embodiment is additionally provided with an observation location detection section  40 , a display position parameter generation section  41 , an observation location manually setting section  42 , and a switching circuit  43 . 
         [0132]    The observation location detection section  40  detects the location of the observer in a plane parallel to the screen SC with respect to the screen SC, and outputs an observation location signal representing the detection result to the display position parameter generation section  41 . It should be noted that in the case in which the projection window W 1  of the first projector  18  is shifted with respect to the screen SC, the observation location can also be obtained as a location with respect to the projection window W 1 . 
         [0133]      FIG. 14A  shows a configuration example of the observation location detection section  40 . As shown in  FIG. 14A , the observation location detection section  40  is composed of an infrared projection section  40   a , an infrared camera  40   b , an image processing section  40   c , and a location determination section  40   d.    
         [0134]    The infrared projection section  40   a  emits an infrared ray with an infrared light emitting diode or the like to illuminate the observer M. The infrared camera  40   b  takes a picture of the observer M and the peripheral area, and outputs image data representing the shooting image to the image processing section  40   c .  FIG. 14B  is a schematic diagram showing the shooting image taken by the infrared camera  40   b . As shown in  FIG. 14B , the observer M viewed from the screen SC side shows up in the shooting image. 
         [0135]    The image processing section  40   c  executes predetermined image processing (e.g., background elimination and binarization process) based on the image data input from the infrared camera  40   b , and outputs the image data on which the binarization process has been executed to the location determination section  40   d . The location determination section  40   d  detects the location of the eyes of the observer M based on the image data input from the image processing section  40   c  to determine the location as the observation location of the observer M, and outputs the observation location signal representing the observation location with two-dimensional coordinates to the display position parameter generation section  41 . 
         [0136]    The display position parameter generation section  41  outputs a position designation signal for designating the position of the extraction range of the image data in the second resolution conversion circuit  13  and the display position of the projection window W 2  of the second projector  19  to the switching circuit  43  based on the observation location signal input from the observation location detection section  40  (the location determination section  40   d ). It should be noted that since the observation location signal input from the observation location detection section  40  only contains the information as the angle viewed from the infrared camera  40   b , the location opposed right to the screen SC varies depending on the observation distance even if the observation locations are the same. Therefore, in the present embodiment, there is adopted a configuration in which the observation distance signal is input from the observation distance measurement section  30  to the display position parameter generation section  41 , thereby correcting the observation location in accordance with the observation distance, thus the location opposed right to the screen SC can be grasped. 
         [0137]    The observation location manually setting section  42  is for setting the observation location by a manual operation, and outputs the observation location signal corresponding to the setting value to the switching circuit  43 . The switching circuit  43  selects either one of the location designation signals input respectively from the display position parameter generation section  41  and the observation location manually setting section  42 , and outputs the selected one to the second resolution conversion circuit  13  and the second projector  19 . 
         [0138]    Meanwhile, as shown in  FIG. 15 , the projection optical system  150  of the optical system  25  in the second projector  19  according to the present third embodiment is provided with an electric lens shifter (a display position control section)  154  to form a configuration in which the display position of the projection window W 2  on the screen SC can be moved in parallel in the horizontal direction and the vertical direction by moving the optical axis of the projection lens  151  in parallel with respect to the exit optical axis of the cross dichroic prism  140 . In other words, the electric lens shifter  154  performs control of the display position of the projection window W 2  corresponding to the position designation signal described above. 
         [0139]    Further, the second resolution conversion circuit  13  in the present third embodiment, similarly to the case of the second embodiment, has the function of controlling the position of the extraction range based on the position designation signal described above in addition to the function of performing the process of extracting the data in the designated range from the image data (with the resolution of QXGA) input from the image memory  11  based on the extraction range designation signal input from the parameter generation section  33 , and the process of converting the resolution according to needs. 
         [0140]    An operation of the display apparatus  3  in the present third embodiment having the configuration described above will hereinafter be explained. It should be noted that hereinafter the explanations of the operation substantially the same as in the second embodiment will be omitted, and the explanations will be presented focusing attention on distinguishing operations in the present third embodiment. 
         [0141]    During the operation of the present display device  3 , the observation location detection section  40  continuously detects the observation location of the observer M with respect to the screen SC, the display position parameter generation section  41  outputs the position designation signal to the second resolution conversion circuit  13  and the second projector  19 . It should be noted that it is assumed that the switching circuit  43  selects the position designation signal of the position parameter generation section  41 . 
         [0142]    Hereinafter, an operation of the second resolution conversion circuit  13  will be explained. Since the operation of the second resolution conversion circuit  13  in the third embodiment is the same as the operation of the flowchart shown in  FIG. 11  explained as the second embodiment except the step S 3 , the explanations will hereinafter be presented focusing attention on the step S 3 . 
         [0143]    In the step S 3 , the second resolution conversion circuit  13  determines the read starting address and the read ending address of the extraction data. 
         [0144]    Specifically, the second resolution conversion circuit  13  determines the read starting address and the read ending address based on the position designation signal. Assuming that the position designation signal contains P, Q values (display position parameters) corresponding to the reading address of X, Y, taking the center of the screen SC or the center of the projection window W 1  of the first projector  18  as the origin, it is enough to provide bias to the address with these display position parameters. 
         [0145]    Specifically, assuming that the extraction range parameter DP takes “0.75” similarly to the second embodiment, the read starting and ending addresses in the X direction and the read starting and ending addresses in the Y direction are obtained as follows. 
         [0146]    Read starting address in the X direction: (2048−1536)/2+P=256+P 
         [0147]    Read ending address in the X direction: 256+1536−1+P=1792+P 
         [0148]    Read starting address in the Y direction: (1536−1153)/2+Q=192+Q 
         [0149]    Read ending address in the Y direction: 192+1153−1+Q=1344+Q 
         [0150]    It should be noted that since reading is performed in the memory area with no data in the case in which the address becomes negative or larger than the address of the image data stored in the image memory  11 , it is enough to set the address to be “0” or the maximum address of the image data in that case. 
         [0151]    By setting the range indicated by the read starting and ending addresses in the X direction and the read starting and ending addresses in the Y direction determined as described above as the extraction range of the data, the data (in other words, the data to be displayed in the projection window W 2  of the second projector  19  with the display position controlled in accordance with the observation location) corresponding to the observation location of the observer M can be extracted. 
         [0152]    On the other hand, the electric lens shifter  154  in the second projector  19  moves the optical axis of the projection lens  151  in parallel in accordance with the position designation signal, thereby controlling the display position of the projection window W 2  of the second projector  19  on the screen SC. 
         [0153]      FIG. 16  shows an example of the image displayed on the screen SC by the distinguishing operation of the third embodiment described above.  FIG. 16  shows the image displayed in the case in which the observer M observes apart of the screen SC located on the lower left of the observer from a location with a certain observation distance. As shown in  FIG. 16 , it is arranged that the display position of the projection window W 2  of the second projector  19  is controlled in accordance with the observation location of the observer M (controlled to be the position where the observer and the screen SC are opposed right to each other), and further, the size, the brightness, and the resolution of the projection window W 2  should be controlled in accordance with the observation location. 
         [0154]    As described above, according to the display apparatus  3  in the present third embodiment, the display position, the size, and the brightness of the projection window W 2  of the second projector  19  can be varied in accordance with the observation location and the observation distance, and at the same time, the display can be continued without varying the size of the object displayed in the projection window W 2  similarly to the case of the second embodiment. Further, since the display position of the projection window W 2  can be moved to the position where the observer is opposed right to the screen SC in accordance with the observation location, it is possible to automatically perform the detailed display of a part of the screen only by getting closer to the part the observer desires to observe in detail. Further, by operating the observation location manually setting section  42  to manually set the part to be displayed in detail, an arbitrary part can be displayed in detail. 
         [0155]    Further, similarly to the second embodiment, it is possible to set the projection window W 2  to be smaller to display the image near the center thereof with the resolution of the input image signal in the case of making observation from a position close to the screen, and to display the image with the display resolution lowered in accordance the observation distance d so as to correspond to the resolution of the eyesight while keeping the apparent view angle approximately constant by enlarging the projection window W 2  in accordance with the distance in the case of making observation from a position away from the screen. Further, since the projection window W 1  of the first projector  18  is displayed constantly, it is possible to make observation from a position close to the screen if it is desired to view the details while constantly grasping the overall picture. 
         [0156]    It should be noted that although the electric lens shifter  154  for moving the optical axis of the projection lens  151  in parallel is used as a measure of moving the display position of the projection window W 2 , as another measure, it is also possible to provide to the second projector  19  an oscillating mechanism for moving the exit optical axis in parallel. On this occasion, although the keystone distortion is caused by the projection angle with the screen SC varying in accordance with the display position, it is possible to adaptively correct the distortion by the keystone distortion correction function of the scaling circuit  21  provided to the second projector  19 . 
       Fourth Embodiment 
       [0157]    Then, a display apparatus according to a fourth embodiment of the invention will be explained. In the third embodiment described above, the case in which the parameter generation section  33  generates the zoom signal, the image quality control signal, and the extraction range designation signal based on the observation distance signal obtained from the observation distance measurement section  30 , and the display position parameter generation section  41  generates the position designation signal based on the observation location signal obtained from the observation location detection section  40  is explained. In contrast, the present fourth embodiment relates to a display apparatus capable of controlling the display position, the size, and the brightness of the second projector  19  by analyzing the characteristic of the content based on the input image signal (image data), and then generating the observation distance signal and the observation location signal in accordance with the analytical result. 
         [0158]      FIG. 17  is a schematic diagram of a configuration of the display apparatus  4  according to the fourth embodiment. It should be noted that in  FIG. 17 , substantially the same constituents as those shown in  FIG. 13  are denoted with the same reference numerals, and the explanations therefor will be omitted. As shown in  FIG. 17 , the display apparatus  4  in the fourth embodiment is additionally provided with a content analysis section  50  and a content parameter generation section  51 . Further, in the fourth embodiment, the observation distance measurement section  30 , the observation distance manually setting section  31 , the switching circuit  32 , the observation location detection section  40 , the observation location manually setting section  42 , and the switching circuit  43  are not necessary, and therefore, are eliminated. 
         [0159]    The content analysis section  50  analyzes the characteristic of the content of the input image signal based on the image data of the input image signal converted into digital data by the A/D converter  10 , and outputs the analytical result to the content parameter generation section  51 . Specifically, the content analysis section  50  is composed of a motion vector detection section  50   a , a spectrum detection section  50   b , and a synthetic determination section  50   c , as shown in  FIG. 18A . 
         [0160]    The motion vector detection section  50   a  detects the vectors of the image based on the image data, and the spectrum detection section  50   b  detects the spectrum (spatial frequency) of the image based on the image data. It should be noted that the detection of the vectors and the spatial frequency is performed for each analysis block obtained by dividing the entire image data into a plurality of pieces as shown in  FIG. 18B . The synthetic determination section  50   c  determines what type of scene is displayed based on the detection results. The content parameter generation section (observation information determination section)  51  determines the observation distance and the observation location of the observer M based on a scene determination result (an analytical result of the content) of the synthetic determination section  50   c , generates the observation distance signal and the observation location signal corresponding to the result, and outputs the observation distance signal to the parameter generation section  33 , and the observation location signal to the display position parameter generation section  41 . 
         [0161]    An operation of the display apparatus  4  in the present fourth embodiment having the configuration described above will hereinafter be explained. It should be noted that hereinafter the explanations of the operation substantially the same as in the third embodiment will be omitted, and the explanations will be presented focusing attention on distinguishing operations in the present fourth embodiment. 
         [0162]      FIG. 19  is a flowchart showing the operation of the content analysis section  50  and the content parameter generation section  51 . It should be noted that in  FIG. 19 , step S 10  shows the operation of the content analysis section  50 , and step S 20  shows the operation of the content parameter generation section  51 . 
         [0163]    As shown in  FIG. 19 , firstly, the motion vector detection section  50   a  detects the vector in each of the analysis blocks of the image data, and then determines whether or not the summation of the vector values of the respective analysis blocks exceeds a predetermined threshold value Vth (step S 11 ). If the result of the step S 11  is “Yes,” namely if the summation of the vector values exceeds the threshold value Vth, it is determined that the image is a moving image, and whether or not the vectors diverge from a certain point is subsequently determined (step S 12 ). 
         [0164]    If the result of the step S 12  is “Yes,” namely if the vectors diverge from a certain point, the synthetic determination section  50   c  determines that the image shows, for example, a forward-moving scene as if looking ahead on a moving vehicle, and outputs the summation of the vector values and the block location of the vanishing point (the point from which the vectors diverge) to the content parameter generation section  51  (step S 13 ). 
         [0165]    On this occasion, in the step S 21 , the content parameter generation section  51  generates the observation distance signal corresponding to the summation of the vector values, and the observation location signal corresponding to the block location of the vanishing point, and then outputs them respectively to the parameter generation section  33  and the display position parameter generation section  41 . 
         [0166]    Since the observer M generally makes observation focusing on the vanishing point in the direction of movement in the forward scene while moving, it is desirable to display an image with a high resolution around the vanishing point. Further, although the observer may try to view detailed information such as a traffic sign, the image with a high resolution is not required because peripheral view is provided to the peripheral area. Further, the higher the moving speed becomes, the smaller the range the observer concentrates on becomes. In other words, the present display apparatus  4  is capable of matching the center of the display position of the projection window W 2  with a high resolution by the second projector  19  with the vanishing point, and further of displaying the peripheral area in the projection window W 1  with a low resolution by the first projector  18 , and therefore, of performing display corresponding to the characteristic of the moving image as described above. 
         [0167]    On the other hand, if the result of the step S 11  described above is “No,” namely if the summation of the vector values does not exceed the threshold value Vth, the spectrum detection section  50   b  detects the spatial frequency of each of the analysis blocks, and at the same time, determines whether or not the analysis block with the spatial frequency higher than a reference value exists (step S 14 ). If the result of the step S 14  is “Yes,” whether or not the analysis blocks with the high spatial frequencies are concentrated in a certain portion is determined (step S 15 ). Further, if the result of the step S 15  is “Yes,” the synthetic determination section  50   c  determines that the image represents the scene as if detailed information is displayed locally, and outputs the number and the locations of analysis blocks corresponding to the detailed information to the content parameter generation section  51  (step S 16 ). 
         [0168]    On this occasion, in the step S 22 , the content parameter generation section  51  generates the observation distance signal corresponding to the number of analysis blocks corresponding thereto, and the observation location signal corresponding to the locations of the analysis blocks, and then outputs them respectively to the parameter generation section  33  and the display position parameter generation section  41 . 
         [0169]    In such a scene that the detailed information is displayed locally, for example, a scene in an education program in which a panel provided with a detailed table and small characters written thereon and an image of an instructor are displayed simultaneously, it is possible to display the detailed information in an eye-friendly manner by displaying the portion of the panel with the projection window W 2  with a higher resolution by the second projector  19 . 
         [0170]    Further, the result of the step S 12 , S 14 , or S 15  is “No,” the synthetic determination section  50   c  determines that the image represents an ordinary scene (step S 17 ), and the content parameter generation section  51  generates the observation distance signal corresponding to the distant location, and the observation location signal corresponding to the central location, and then outputs them respectively to the parameter generation section  33  and the display position parameter generation section  41 . 
         [0171]    In other words, in the case of the image (an ordinary scene) without any features to pay attention to, by setting the observation distance to be the distant location, and setting the observation location to be the center, the display position, the size, the brightness, and the resolution of the projection window W 2  of the second projector  19  are converted to be the same levels as those of the projection window W 1  of the first projector  18 , and normal single window display is preformed. It should be noted that as described in the explanations of the second embodiment, on this occasion, since the projection window W 1  of the first projector  18  becomes black due to the blanking signal, the degradation in the image quality due to the overlap between the projection windows can be prevented. 
         [0172]    As explained above, according to the present first through fourth embodiments, the function equivalent to the high-resolution display can be realized at relatively low cost. Further, since the partial detailed display can be performed while varying the size, the resolution, and the brightness in accordance with the distance and the location of the observer with respect to the screen SC with the overall picture displayed, the display corresponding to the natural human action of getting away from the screen for viewing the overall picture while getting closer to the screen for viewing the details can be performed. 
         [0173]    The display apparatuses  1  through  4  in the first through the fourth embodiments described above can be applied to a driving simulator, a ship simulator, an airplane simulator, and so on. Further, in the future, in the case of executing the computerized desktop work while projecting documents on the desk, the display apparatuses  1  through  4  can also be used in the case in which it is not realistic to realize the resolution as high as printed materials in the entire document but only a certain portion of the document to pay attention to, for example, is displayed with the high resolution. On this occasion, since the two projectors are physically separated, and low light output is allowed in the detailed display section, there is a possibility of using a projector with an LED light source or a laser light source, or even a scan projector. By adopting the configuration described above, the whole size of the apparatus can also be reduced. 
         [0174]    It should be noted that although in the first through the fourth embodiments, the explanations are presented exemplifying the case of using the two projectors, it is also possible to adopt a configuration in which a liquid crystal light valve LV 1  for the projection window W 1  and a liquid crystal light valve LV 2  for the projection window W 2  are provided to a single projector, the illumination light of a light source L is blanched by an optical branching prism PBS and a mirror M 1  to input the blanched light in the liquid crystal light valve LV 1  and the liquid crystal light valve LV 2 , and the light beams emitted from the liquid crystal light valve LV 1  and the liquid crystal light valve LV 2  are combined by a combining prism PM and a mirror M 2  to output the light beams. Further, the position of the liquid crystal light valve LV 2  is arranged to be able to be controlled by a position driving section DV. By adopting such a configuration, as shown in  FIG. 20B , it becomes possible to display the projection window W 1  and the projection window W 2  with a single projector. 
         [0175]    Further, although the explanations are presented in the first through the fourth embodiments exemplifying the case in which one projection window W 2  (the second window) is displayed overlapping with the projection window W 1  (the first window), this is not a limitation, but it is also possible to adopt a configuration of overlapping a plurality of second windows with the first window, namely a configuration provided with a plurality of second light modulation sections. 
         [0176]    The entire disclosure of Japanese Patent Application No. 2008-268632, filed Oct. 17, 2008 is expressly incorporated by reference herein.