Abstract:
A projecting a plurality of red pixels, green pixels, and blue pixels to display a color image on a screen. First and second green pixels differing in their positions correspond to red and blue pixels projected on the screen.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a projection system which projects a color image on a screen utilizing projector devices. 
   2. Description of the Related Art 
   Conventionally, in order to display a highly precise image on a large screen, a projection system has been proposed, in which a plurality of projector devices are used to project a color image on a screen. 
     FIG. 8  shows a conventional projection system in which the same projector devices are arranged. 
   As shown in  FIG. 8A , this projection system is configured so that four (2×2: first to fourth) projector devices including a first projector device  101  and a second projector device  102  are arranged. In a screen  103 , images projected from the first and second projector devices  101  and  102  are displayed on neighboring first and second areas  103   1  and  103   2 . 
   In the screen  103  shown in  FIG. 8B , first to fourth areas  103   1  and  103   4  are shown, on which images are displayed through the first to fourth projector devices. The first to fourth projector devices is assigned to display the areas  103   1  and  103   4 , each of areas  103   1  and  103   4  being a quarter of the screen  103 . 
     FIG. 9  shows a projection system, which projects images from the same projector devices on the same area. 
   As shown in  FIG. 9A , four (2×2: first to fourth) projector devices including a first projector device  111  and a second projector device  112  display images on the same area of a screen  113 . On the screen  113 , pixels projected from respective projector devices are arranged so that these pixels are shifted 0.5 pixels as for the minimum pixel unit with each other. Consequently, as a result, the image displayed on the screen is assumed to be equal in the case where the pixel size becomes half, which leads to a highly precise image. 
   When a part of an area  113   a  on the screen  113  shown in  FIG. 9B  is enlarged, as shown in  FIG. 9C , the pixels from the first to fourth projector devices are shifted 0.5 pixels with each other. Specifically, the first pixel from the first projector device  111  depicted as the symbol “circle”, the second pixel from the second projector device  112  depicted as the symbol “star”, the third pixel from the third projector device (not shown) depicted as the symbol “triangle”, and the fourth pixel from the fourth projector device (not shown) depicted as the symbol “asterisk” are arranged so that the positions are shifted 0.5 pixels with each other in the horizontal direction and/or the vertical direction. 
   In the projection system where the projector devices are arranged as shown in  FIG. 8A , precise matching is required at the joint (depicted as broken line a in  FIG. 8B ) between the images assigned to the respective projector devices. Also, when the number of the pixels is doubled, the number of the projector devices should be increased by a factor of four, leading to a large-scale system. 
   In the projection system shown in  FIG. 9A  where images are projected from a plurality of the projector devices on the same area, it is difficult to perfectly shift the images 0.5 pixel over the entire area of the display because of the influence of the deformation of the lens between the projector devices. 
   An object of the present invention is to provide a projection system, which is composed of a small number of constituents and which can display a highly precise image. 
   SUMMARY OF THE INVENTION 
   The projection system of the present invention projects a plurality of red pixels, green pixels, and blue pixels so as to display a color image on a screen by projecting. In the projection system of the present invention, first and second green pixels differing in their positions correspond to red and blue pixels projected on the screen. 
   Preferably, the positions of the first and second green pixels are shifted 0.5 pixels of the minimum pixel unit in the horizontal direction and/or the vertical direction. For example, if they are shifted 0.5 pixels in both the horizontal and vertical directions, it is recognized that the resolutions in both the horizontal and vertical directions are doubled, respectively. 
   Because the visibility in humans is the best in the green region, when green pixels are shifted 0.5 pixels to place the pixels in a doubled manner, substantially high resolution can be recognized. This can display a high resolution and highly detailed image by the constitution substantially resembling that of the conventional projector devices. By enlarging the image, a highly detailed image can be realized on a large screen. 
   The projection system according to the present invention possesses red light-modulation means, which modulates a red pixel, blue light-modulation means which modulates a blue pixel, first green light-modulation means, which modulates first green lights, and second green light-modulation means, which modulates a second green pixel, and the projection system projecting the red pixels, blue pixels, and first and second green pixels. 
   According to one preferred embodiment, the projection system possesses a first projector device having the red light-modulation means and the blue light-modulation means, and a second projector device having the first green light-modulation means and the second green light-modulation means. 
   According to another preferred embodiment, the projection system according to the present invention possesses red light and blue light-modulation means, which simultaneously modulates red and blue pixels, instead of the separate red light-modulation means and the blue light-modulation means , and red light and blue light-modulation means includes filters for red lights and blue lights corresponding to the red pixel and the blue pixel. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a projector device according to the first embodiment of the present invention. 
       FIG. 2  shows a projector device according to the second embodiment of the present invention. 
       FIG. 3  shows a projector device according to the third embodiment of the present invention. 
       FIG. 4  shows a first projector device according to the third embodiment of the present invention. 
       FIG. 5  shows a second projector device according to the third embodiment of the present invention. 
       FIG. 6  shows the arrangement of a first green pixel and a second green pixel projected from the second projector device. 
       FIG. 7  shows a processing of the image signals in the projector device according to the third embodiment. 
       FIGS. 8A and 8B  show a conventional projection system in which the same projector devices are arranged. 
       FIGS. 9A ,  9 B and  9 C show a projection system, which projects images from the same projector devices on the same area. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the projection systems according to the present invention will be described, referring to the attached drawings. 
     FIG. 1  shows a projector device  10  according to the first embodiment of the present invention. 
   The projector device  10  possesses four sheets of liquid crystal panels. Specifically, the projector device  10  possesses one liquid crystal panel  17  for red light, which modulates red lights (red light-modulation means), and one liquid crystal panel  16  for blue light, which modulates blue lights (blue light-modulation means). Also, the projector device  10  possesses a liquid crystal panel  18  for first green light, which modulates first green lights (first green light-modulation means), and a liquid crystal panel  19  for second green light, which modulates second green lights (second green light-modulation means). 
   The liquid crystal panel  17  for red light, the liquid crystal panel  16  for blue light, and the liquid crystal panels  18  and  19  for first and second green lights have the same resolution. The first and second green pixels projected on a screen through the first and second green lights are shifted 0.5 pixels with each other. These liquid crystal panels  16 ,  17 ,  18 , and  19 , which are used, are light transmission type liquid crystal elements. In the embodiments described later on, light transmission liquid crystal elements are used in the type liquid crystal panels. 
   The projector device  10  has a lamp  11  for emitting a white light, a first dichroic mirror  12  in which the white light emitted from the lamp  11  enters, a second dichroic mirror  13 , in which the light transmitted through the first dichroic mirror  12  enters, a half mirror  14 , in which a green light (G) transmitted through the second dichroic mirror  13  enters, and a first mirror  15  in which a blue light (B) reflected at the first dichroic mirror  12  enters. 
   Also, the projector device  10  possesses the liquid crystal panel  16  for blue light (blue light-modulation means), in which a blue light reflected at the first mirror  14  enters, the liquid crystal panel  17  for red light (red light-modulation means), in which a red light (R) reflected at the second dichroic mirror  13  enters, the liquid crystal panel  18  for first green light (first green light-modulation means), in which a first green light (G 1 ) transmitted through the first half mirror  14  enters, and liquid crystal panel  19  for second green light (second green light-modulation means), in which a second green light (G 2 ) reflected at the first half mirror  14  enters. 
   Furthermore, the projector device  10  possesses a second mirror  20 , in which a light enters from the liquid crystal panel  18  for first green light, a third dichroic mirror  21 , in which lights enter from the liquid crystal panel  16  for blue light and the liquid crystal panel  17  for red light, a fourth dichroic mirror  22 , in which the lights enter from the liquid crystal panel  19  for second green light and the third dichroic mirror  21 , a second half mirror  23 , in which the lights enter from the second mirror  20  and the fourth dichroic mirror  22 , and a projection lens  24 , in which a light enters from the second half mirror. 
   The white light emitted from the lamp  11  enters the first dichroic mirror  12 , in which a red light and a green light are transmitted and in which a blue light is reflected. The red light and the green light transmitted through the first dichroic mirror  12  enter the second dichroic mirror  13 , in which the green light is transmitted and at which the red light is reflected. The green light transmitted through the second dichroic mirror  13  enters the first half mirror  14 , in which a half of the green light is transmitted and at which the remaining half of the green light is reflected. The blue light reflected at the first dichroic mirror  12  enters the first mirror  15 , which is reflected. 
   The blue light reflected at the first mirror  15  enters the liquid crystal panel  16  for blue light, which is then modulated. The red light reflected at the second dichroic mirror  13  enters the liquid crystal panel  17  for red light, which is then modulated. The half of the green light transmitted through the first half mirror  14  enters the liquid crystal panel  18  for a first green light, which is then modulated. The remaining half of the green light reflected on the first half mirror  14  enters the liquid crystal panel  19  for second green light, which is then modulated. 
   The green light having been modulated at the liquid crystal panel  18  for first green light enters the second mirror  20  and is reflected. The blue light having been modulated at the liquid crystal panel  16  for blue light enters the third dichroic mirror  21  and is transmitted. The red light having been modulated at the liquid crystal panel  17  for red light enters the third dichroic mirror  21  and is reflected. The blue light and the red light from the third dichroic mirror  21  enters the fourth dichroic mirror  22  and are transmitted. The second green light having been modulated through the liquid crystal panel  19  for second green light enters the fourth dichroic mirror  22 , and is reflected. The first green light reflected at the second mirror  20  enters the second half mirror  23 , and part of the green light is reflected. The blue light, red light, and the green light from the fourth dichroic mirror  22  enter the second half mirror  23 , and parts of them are transmitted. The light from the half mirror  23  enters the projection lens and then is projected on a screen (not shown). 
   The blue light, the red light, and the green light are projected on the same region on the screen (not shown) through the projection lens  24  to make up an image. On the screen, the first and second green pixels corresponding to the first and second green lights having been modulated through the first and second liquid crystal panels  18  and  19  for green light are arranged so that they are shifted 0.5 pixels as the minimum pixel unit in the horizontal direction and/or the vertical direction. Because green is the maximum at the human&#39;s visible region, when the green pixels are shifted 0.5 pixels so as to arrange the pixels in a doubled manner, substantial high resolution is recognized. This makes it possible to realize a highly detailed image with a high resolution only by the constitution substantially resembling that of the conventional projector devices. By enlarging the image, a highly detailed image can also be realized on a large screen. 
   In the following embodiments, the first and second green pixels are shifted 0.5 pixels similar to the foregoing embodiment. Specific arrangements of the first and second green pixels will be described later on by referring to FIG.  6 . 
     FIG. 2  shows a projector device  30  according to the second embodiment of the present invention. 
   In the projector device  30  in the second embodiment, parts corresponding to those of the projector device  10  are referred to the same symbols or numbers. 
   The projector  30  possesses three liquid crystal panels, i.e., a liquid crystal panel  32  for red and blue lights, which simultaneously modulates red and blue lights (red light and blue light-modulation means), a liquid crystal panel  18  for first green light, which modulates first green lights (first green light-modulation means), and a liquid crystal panel  19  for second green light, which modulates second green lights (second green light-modulation means). 
   The liquid crystal panel  32  for red and blue lights, and the liquid crystal panels  18  and  19  for first and second green lights have the same resolution. The first and second green pixels projected on a screen through the first and second green lights are shifted 0.5 pixels with each other. The red light and blue light-modulation means may be configured to include a filter  33  for red and blue lights. 
   The projector device  30  has a lamp  11  for emitting a white light, a first dichroic mirror  31  in which the white light emitted from the lamp  11  enters, and a first half mirror  14 . 
   Also, the projector device  30  possesses the liquid crystal panel  32  for red and blue lights (red light and blue light-modulation means), in which a red light (R) and blue light (B) reflected at the first dichroic mirror  31  enter, a filter  33  for red and blue lights (red light and blue light-modulation means), in which the red light and the blue light having been modulated through the liquid crystal panel  32  for red and blue lights enters, the liquid crystal panel  18  for first green light (first green light-modulation means), in which a first green light (G 1 ) transmitted through the first half mirror  14  enters, and liquid crystal panel  19  for second green light (second green light-modulation means), in which a second green light (G 2 ) reflected at the first half mirror  14  enters. 
   Furthermore, the projector device  30  possesses a first mirror  15 , in which the light enters from the filter  33  for red light and blue light enter, a second mirror  20 , in which the first green light enters from the liquid crystal panel  18  for first green light, a second dichroic mirror  34 , in which lights enter from the second mirror  15  and the liquid crystal panel  19  for second green light, a second half mirror  23  in which lights enter from the second mirror  20  and the second dichroic mirror  34 , and a projection lens  24  in which a light enters from the second half mirror  23 . 
   The white light emitted from the lamp  11  enters the first dichroic mirror  31 , in which a green light is transmitted and at which a red light and a blue light are reflected. The green light transmitted through the first dichroic mirror  31  enters the first half mirror, in which half of the green light is transmitted and at which the remaining half of the green light is reflected. 
   The red light and blue light reflected at the first dichroic mirror  31  are modulated through the liquid crystal panel  32  for red and blue lights, and filtered through the filter  33  for red light and blue light. The half of the green light transmitted through the first half mirror  14  is modulated through the liquid crystal panel  18  for first green light. The remaining half of the green light reflected on the first half mirror  14  is modulated through the liquid crystal panel  19  for the second green light. 
   The red light and the blue light filtered through the filter  33  for red light and blue light enter the first mirror  15  and reflected. The green light having been modulated through the liquid crystal panel  18  for first green light enters the second mirror  20  and is reflected. 
   The red light and the blue light reflected at the first mirror  15  enter the second dichroic mirror  34 , and are transmitted. The second green light having been modulated at the liquid crystal panel  19  for the second green light enters the second dichroic mirror  34  and is reflected. The first green light reflected at the second mirror  20  enters the second half mirror  23 , and a part of the green light is reflected. The light from the second dichroic mirror  34  enters the second half mirror  23 , and a part of the light is transmitted. The light from the second half mirror  23  enters the projection lens  24 , and is projected on a screen (not shown). 
   Similar to the first embodiment described previously, the first and second green pixels corresponding to the first and second green lights having been modulated through the first and second liquid crystal panels  18  and  19  for green light are positioned on the screen where they are shifted 0.5 pixels of the minimum pixel unit in the horizontal direction and/or the vertical direction. This makes it possible to realize a highly detailed image with high resolution. The constitution of the second embodiment is much smaller than that of the first embodiment. 
     FIG. 3  shows a third embodiment where lights are projected on a screen through a first projector device  50  and a second projector device  70 . 
   A first projector device  50  projects a red (R) light, and a blue light (B) on a screen. A second projector  70  projects a green light (G) on the screen  80 . The images projected from the first and second projector devices  50  and  70  are projected on the same position on the screen  80 . 
     FIG. 4  shows a first projector device  50  according to the third embodiment of the present invention. 
   The first projector device  50  possesses two liquid crystal panels, i.e., a liquid crystal panel  56  for red light (red light-modulation means), and a liquid crystal panel  55  for blue light (blue light-modulation means). 
   In the projector device  50 , a part  62  for modulating a green light (G) does not actuate or the projector device  50  may have no part  62  for modulating a green light (G). In this embodiment, first, the configuration where the part  62  for modulating a green light (G) is provided will be described. 
   The first projector device  50  has a lamp  51  for emitting a white light, a first dichroic mirror  52  in which the white light emitted from the lamp  51  enters, a second dichroic mirror  53 , in which the light from the first dichroic mirror  52  enters, and a first mirror  54  in which a blue light (B) reflected at the first dichroic mirror  52  enters. 
   Also, the first projector device  50  possesses the liquid crystal panel  55  for blue light (blue light-modulation means), in which a blue light reflected at the first mirror  54  enters, the liquid crystal panel  56  for red light (red light-modulation means), in which a red light (R) reflected at the second dichroic mirror  53  enters, and the liquid crystal panel  57  for green light, in which a green light transmitted through the second dichroic mirror  53  enters. 
   Furthermore, the first projector device  50  possesses a third dichroic mirror  59 , in which lights enter from the liquid crystal panel  55  for blue light and the liquid crystal panel  56  for red light, and a half mirror  60  in which the lights enter from the first mirror  58  and the third dichroic mirror  59 . 
   The white light emitted from the lamp  51  enters the first dichroic mirror  52 , in which a red light and a green light are transmitted and at which a blue light is reflected. The red light and the green light transmitted through the first dichroic mirror  52  enter the second dichroic mirror  53 , in which the green light is transmitted and at which the red light is reflected. The blue light reflected at the first dichroic mirror  52  enters the first mirror  54  and is reflected. 
   The blue light reflected at the first mirror  54  enters the liquid crystal panel  55  for blue light, which is then modulated. The red light reflected at the second dichroic mirror  53  enters the liquid crystal panel  56  for red light, which is then modulated. The green light transmitted through the second dichroic mirror  53  enters the liquid crystal panel  57  for green light, which is then modulated. 
   The light having been modulated at the liquid crystal panel  55  for blue light enters the second dichroic mirror  59  and is transmitted. The light having been modulated at the liquid crystal panel  56  for red light enters the second dichroic mirror  59  and is reflected. The blue light and the red light from the second dichroic mirror  59  enter the half mirror  60 , and parts of them are transmitted. The green light reflected at the second mirror enters the half mirror  60 , and a part of the light is reflected. The light from the half mirror  60  enters the projection lens  61  and is projected on a screen  80 . 
   Because the first projector device  50  only projects a red light and a blue light, the part  62  for modulating a green light is not actuated or is not provided. For example, the liquid crystal panel  57  for green light always inhibits th e green light from t he second dichroic mirror  53  to be transmitted. Otherwise, the part  62  for modulating a green light is taken out of the first projector device  50 . 
     FIG. 5  shows a second projector device  70  according to the third embodiment of the present invention. 
   The second projector device  70  possesses two series of the first green light-modulation means, i.e., a liquid crystal panel  74  for first green light (first green light-modulation means), which modulates a first green light (G 1 ), and a liquid crystal panel  75  for second green light (second green light-modulation means), which modulates a second green light (G 2 ). These liquid crystal panels  74  and  75  for green lights have the same resolution as that of the liquid crystal panel  56  for red light and that of the liquid crystal panel  55  for blue light. 
   The second projector device  70  has a lamp  71  for emitting a white light, a filter  72  for green light in which the white light emitted from the lamp  71  enters, a half mirror  72 , in which a green light (G) transmitted through the filter for green light enters, a liquid crystal panel  74  for first green light in which a first green light transmitted through the half mirror  73  enters, and a liquid crystal panel  75  for second green light in which a second green light reflected at the half mirror  73  enters. 
   Also, the second projector device  70  possesses a first mirror  76 , in which the first green light from the liquid crystal panel  74  for first green light enters, a second mirror  77 , in which the second green light from the liquid crystal panel  75  for second green light enters, a second half mirror  78 , in which green light enters from the first mirror  76  and the second mirror  77 , and a projection lens  79 , in which the green light enters from the second half mirror  78 . 
   The white light emitted from the lamp  71  enters the filter  72  for green light, through which only the green light is transmitted. The green light transmitted through the filter  72  for green light enters the first half mirror  73 , in which half of the green light is transmitted and at which the remaining half of the green light is reflected. The first green light transmitted through the first half mirror  73  enters the liquid crystal panel  74  for first green light and is modulated. The second green light reflected at the first half mirror  73  enters the liquid crystal panel  75  for second green light and is modulated. 
   The first green light having been modulated through the liquid crystal panel  74  for first green light enters the first mirror  76  and is reflected. The second green light having been modulated through the liquid crystal panel  75  for second green light enters the second mirror  77  and is reflected. The first green light reflected at the first mirror  76  enters the second half mirror  78 , and a part of the light is reflected. The second green light reflected at the second mirror  77  enters the second half mirror  78 , and a part of the light is transmitted. The light from the half mirror  78  enters the projection lens  71 , and is projected on the screen  80 . 
     FIG. 6  shows the arrangement of pixels projected through the second projector device  70 . In this figure, the symbol “circle” represents the first green light (G 1 ) modulated through the liquid crystal panel  74  for first green light, and the symbol “asterisk” represents the second green light (G 2 ) modulated through the liquid crystal panel  75  for second green light. The centers of the first and second pixels are overlapped at the position where they are shifted 0.5 pixels, i.e., ½ of the minimum pixel unit pitch, in the horizontal direction and the vertical direction. 
   As described previously, because the visibility in humans is at maximum for the green light, when the arrangement of the pixels is doubled by shifting the green pixels 0.5 pixels, it is sensed by the humans&#39; eyes that the resolutions both in the horizontal direction and the vertical direction are doubled. Consequently, a substantial high resolution is recognized and an image on a large display can be realized. 
   The positional relationship between the pixels from the first and the second green lights can be maintained as it is, if it is adjusted at the time of assembling the second projector device  70 . Because the first projector device  50 , which projects red and blue lights and the second projector device  70 , which projects the first and second green lights have a construction different from each other, they should be aligned. A technique for convergence adjustment, which has conventionally been performed in a CRT, is available for this alignment, and, thus, the alignment can easily be performed. 
   In this third embodiment, the conventional projector device is applied to the first projector device  50 , which projects a red light and a blue light, and the second projector device  70 , which project green lights, is separately provided. Consequently, only the second projector device may be added to the conventional projector device, the projection system according to the present invention can be constructed, meaning that high resolution can be realized only with small constitution. 
     FIG. 7  shows a processing of the image signals in the projector device according to the third embodiment. 
   When a number of pixels of each liquid crystal panel are M in length and N in width (M×N), as for green light, an image comprising 2M in length and 2N in width (2M×2N) can be displayed in high detail by projecting green light which has been shifted by half pixel pitch. 
   A green (G) image ( 8 I) having a number of pixels of 2M×2N is subjected to a sampling processing  70  where pixels corresponding to the first green light (G 1 ) and the second green light in  FIG. 6  are extracted to form a signal  83  for the first green light and a signal  84  for the second green light in the second projector device  70 . 
   A red (R) image having a number of pixels of 2M×2N is subjected to processing where an M×N image is taken by a low pass filter (LPF)  86  to form a signal ( 87 ) for pixel of the red light in the first projector device  50 . 
   A blue (B) image having a number of pixels of 2M×2N is subjected to processing where an M×N image is taken by a low pass filter (LPF)  89  to form a signal ( 90 ) for pixel of the blue light in the first projector device  50 . 
   By performing such signal processing constructed as described above, flicker inherent to the liquid crystal projection system can be moderated. Specifically, because the flicker occurs due to the characteristic difference between a positive signal and a negative signal applied to the liquid crystal panel, they can be contradicted by making quantities of light from both polar liquid crystal panels equal. In this embodiment, it can be performed by selecting appropriate signals in sub-sampling and low pass filters. 
   As described above, according to the present invention, a highly precise image can easily be constructed. Specifically, as compared with the conventional projection system where a plurality of the projectors are arranged, the image obtainable from the present invention is seamless, the projection system of the present invention is not required to make an adjustment of the seam. In such a conventional projection system, in order to double the resolution, 2×2, i.e., four, projector devices is required, whereas the projection system according to the present invention, only two projectors are required for doubling the horizontal and vertical resolutions. 
   In comparison with the conventional projection system where images are projected through a plurality of the projectors on the same region, because the same projection lens is used for the green light in the present invention, the positional relation is not shifted due to the deformation of the lens and, thus, the high detail image can be maintained over the entire area of the display in the projection system of the present invention. 
   While the embodiments of the present invention have been described, it should be noted that the present invention is not restricted to these embodiments. For example, a transmission liquid crystal element has been used as the modulation means in these embodiments, the present invention is not restricted thereto. A DMD (digital mirror device) and reflective type liquid crystal elements may be used as the modulation means.