Abstract:
A projection display device comprises a plurality of light sources which produce different primary colors of light, a plurality of display units each of which is driven by a video signal corresponding to one of the primary colors, receives light from one of the light sources which produces light corresponding to the one of the primary colors, and outputs video image light modulated by the video signal, a projection unit which projects video image light output from the display units, and a light source control unit configured to control the amount of light produced by each of the light sources independently.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-167155, filed Jun. 7, 2002, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to improvements in a projection display device which projects an optical image onto a screen for video display. 
   2. Description of the Related Art 
   In recent years, with the widespread use of information terminals for the home, such as personal computers, and the practical use of high-definition television, the demand has increased for displaying video images on a larger screen with higher brightness and resolution. To meet such a demand, the development of projection display devices, such as liquid crystal projectors, is accelerated at present. 
   A projection display device comprises: three light sources each corresponding to a respective one of a plurality of primary colors, for example, red (R), green (G) and blue (B); three liquid crystal display panels each displaying a video image corresponding to a respective one of the R, G, and B color components; an optical path which directs colored light from each of the light sources to a respective one of the liquid crystal display panels, outputs video image light modulated by the display panels and combines the video image light from the display panels; and a projection lens which projects the combined video image light onto a screen. 
   As it stands, there is much room to improve the details of such a projection display device. One of the improvements is to further enhance the quality of video images displayed on the screen. There is a strong demand for developing such a technique to increase the video image quality as soon as possible. 
   For example, Japanese Unexamined Patent Publication No. 7-222185 discloses a projection liquid crystal display device which makes it possible to adjust the color temperature of at least one of a plurality of light sources so that chromaticity can be adjusted and sufficiently bright images can be obtained. As a color temperature adjustment method, there is disclosed an example of providing a filter that lowers colored light within a given waveband. This makes it easy to increase the brightness and adjust the color temperature. 
   However, the display device disclosed is complex in structure because of the necessity of a special filter for color temperature adjustment as a separate part. 
   BRIEF SUMMARY OF THE INVENTION 
   According to an aspect of the present invention there is provided a projection display device comprising: a plurality of light sources configured to produce different primary colors of light; a plurality of display units each of which is configured to be driven by a video signal corresponding to one of the primary colors, receive light from one of the light sources which produces light corresponding to the one of the primary colors, and output video image light modulated by the video signal; a projection unit configured to project video image light output from the display units; and a light source control unit configured to control the amount of light produced by each of the light sources independently. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  shows an example of an optical system of a projection display device according to an embodiment of the present invention; 
       FIG. 2  is a block diagram of the signal processing system of the projection display device in the embodiment of the present invention; 
       FIG. 3  is a flowchart illustrating a characteristic operation of the projection display device in the embodiment of the present invention; and 
       FIG. 4  shows another example of an optical system of the projection display device in the embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A projection display device according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings.  FIG. 1  is a schematic diagram of the projection display device and mainly illustrates its optical system in particular. In  FIG. 1 , a light source  11  is adapted to emit red light. A liquid crystal (LC) display panel  12  is placed in front of the light source  11 . 
   The liquid crystal display device  12  has a video display screen driven by a red component video signal. When illuminated with the red light from the light source  11 , the liquid crystal display panel  12  outputs video image light modulated by the red component video signal. 
   Likewise, there is provided a light source  13  which corresponds to the green waveband component of light. A liquid crystal display panel  14  is placed in front of the light source  13 . Further, a light source  15  is provided which corresponds to the blue waveband component of light. A liquid crystal display panel  16  is placed in front of the light source  15 . 
   The liquid crystal display panels  14  and  16  are driven by green and blue component video signals, respectively. When illuminated with the green and blue light from the light sources  13  and  15 , the liquid crystal display panels  14  and  16  respectively output video image light modulated by the green and blue component video signals. 
   The red, green and blue light components transmitted through the liquid crystal display panels  12 ,  14  and  16  are incident on a cross-prism  17  and combined. After that, the output light from the cross-prism  17  is diffusion-projected by a projection lens  18  onto a screen  19  for video image display. 
     FIG. 2  shows the signal processing system of the projection display device. A television signal receiving section  20  is controlled by a set controller  21  including a microcomputer to select a desired television (TV) signal from among a plurality of received television signals and output it to a video signal processing section  22 . 
   The video signal processing section  22  performs demodulation processing on the input television signal to produce R, G, and B video signals, which in turn are applied to liquid crystal display signal processing sections  23 ,  24  and  25 , respectively. 
   The liquid crystal display signal processing sections  23 ,  24  and  25  convert the input R, G and B video signals into liquid crystal display signals suitable for video display on succeeding liquid crystal display panels  12 ,  14 , and  16 . Thereby, video images corresponding to the R, G and B waveband components are displayed on the liquid crystal display panels  12 ,  14 , and  16 , respectively. 
   The video signal processing section  22  outputs to a light source controller  26  control signals for adjusting the amounts of light emitted by light sources  11 ,  13 , and  15  to suit the video signals. The light source controller  26  is also supplied from the set controller  21  with setting data which conforms to a display mode. 
   Based on the input control signal and setting data, the light source controller  26  produces and outputs light source adjustment data to light source adjustment sections  27 ,  28  and  29  which drives the R, G and B light sources  11 ,  13 , and  15 , respectively. Based on the input light source adjustment data, each of the light source adjustment sections  27 ,  28  and  29  produces and applies a light adjustment signal to a corresponding respective one of the light sources  11 ,  13 , and  15 . Each of the light sources emits light accordingly. 
     FIG. 3  is a flowchart illustrating characteristic operations of the projection display device configured as described above. First, when the operation of the display device is started, a television signal selected by the television signal receiving section  20  is input to the video signal processing section  22 . 
   Then, in step S 12 , the video signal processing section  22  recovers R, G and B video signals from the input television signal and adjusts the level of each of these video signals. In this example, the R, G and B video signals are controlled so that each of them is level-adjusted at a constant amplification factor. 
   The level-adjusted R, G and B video signals from the video signal processing section  22  are applied to the liquid crystal display signal processing sections  23 ,  24  and  25 , respectively. Thereby, liquid crystal display signals to be displayed on the liquid crystal display panels  12 ,  14  and  16  are produced as described previously. 
   After that, in step S 13 , the liquid crystal display signal processing sections  23 ,  24  and  25  adjust to the levels of the R, G and B liquid crystal display signals, respectively. In this example, each of the R, G and B liquid crystal display signals is adjusted to have the same level as the video signals. 
   In subsequent step S 14 , the video signal processing section  22  outputs to the light source controller  26  control signals for adjusting the amounts of light produced by the light sources  11 ,  13  and  15 . The light source controller  26  responds to the input control signals and setting data from the set controller  21  to produce R, G and B light source adjustment data, which are output to the light source adjustment sections  27 ,  28 , and  29 . 
   In step S 15 , the light source adjustment sections  27 ,  28  and  29  respond to the input light source adjustment data to produce R, G and B light source adjustment signals, which are output to the light sources  11 ,  13  and  15 , respectively. It therefore becomes possible to vary the amount of light produced by each of the light sources  11 ,  13  and  15  individually. 
   In this example, as shown in  FIG. 2 , the G light source adjustment signal is controlled so that its level becomes lower than those of the R and B light source adjustment signals. This means that the amount of light emitted by the light source  13  has been set lower than those of the other light sources  11  and  15 , in other words, the G luminance level has been set lower than the R and B luminance levels. Thereby, the luminance levels can be adjusted according to the characteristics of the liquid crystals in the liquid crystal panels  12 ,  14 , and  16 , allowing the R, G and video components to be displayed uniformly. 
   That is to say, the light source controller  26  and the light source adjustment sections  27 ,  28 , and  29  form a control unit which controls the amount of light of each of the light sources  11 ,  13 , and  15  individually. 
   According to the embodiment described above, the R, G and B luminance levels can be controlled not only by adjusting the levels of the liquid crystal display signals for the R, G, and B liquid crystal display panels  12 ,  14  and  16  but also by varying the amount of light produced by each of the R, G and B light sources  11 ,  13 , and  15  individually. 
   Thus, by combining two types of luminance adjustment means to make the R, G and B luminance levels adjustable, it becomes possible to achieve luminance control of displayed video images which has not existed heretofore. Thereby, it becomes possible to improve the quality of video images displayed on the screen  19  readily with a straightforward configuration. 
   In addition, white balance adjustment and luminance adjustment can be made by making the amount of light of each of the light sources  11 ,  13  and  15  corresponding to the R, G and B waveband components variable independently. 
   Furthermore, the amounts of light of the R, G and B light sources  11 ,  13  and  15  can be adjusted dynamically to suit a video signal to be displayed. For example, for a dark video image, the amounts of light of the light sources can be lowered correspondingly to display that video image more darkly. 
   Moreover, it is also possible to make luminance adjustment to suit a preset video image display mode. That is, in a theater mode, making, say, blue and/or red color brighter allows a video image displayed on the screen  19  to become close to a video image as viewed in a movie theater; therefore, desired color reproduction becomes enabled by controlling the amount of light of a specific light source or sources according to a display mode. 
   Furthermore, the luminance control based on control of the amounts of light of the light sources  11 ,  13  and  15  allows the effective use of the dynamic range of a video signal. In addition, control of the amounts of light of the light sources  11 ,  13  and  15  allows the power consumption to be reduced in comparison with the circumstance that each light source is driven to produce the maximum amount of light as hitherto. 
   Referring now to  FIG. 4  there is illustrated another example of an optical system of a projection display device. Though  FIG. 4  mainly illustrates the optical system, the signal processing system remains unchanged from that of FIG.  2 . 
   In the optical system of  FIG. 4 , laser sources  30 ,  31  and  32  are provided which correspond to R, G and B waveband components, respectively. Beams of light produced by the laser sources  30 ,  31  and  32  are transmitted through an optical fiber cable  33 . The output light of the optical fiber cable  33  passes through a condenser lens  34  and is then separated by a cross-dichroic mirror  35  into the R and G components and the B component. 
   The R and G components of light are reflected by a mirror  36  onto a dichroic mirror  37 , which separates the incident light into the R and G components. The R light is directed through a beam splitter  38  onto a liquid crystal display panel  39  to display a video image corresponding to the R component. The G light is directed through a beam splitter  40  onto a liquid crystal display panel  41  to display a video image corresponding to the G component. 
   On the other hand, the B component of light separated by the cross-dichroic mirror  35  is reflected by a mirror  42  and then directed through a beam splitter  43  onto a liquid crystal display panel  44 , whereby a video image corresponding to the B component is displayed. 
   The liquid crystal display panels  39 ,  41  and  44  modulate the incident light with R, G and B video signals and reflect the modulated light onto the beam splitters  38 ,  40  and  43 . The R, G and B video image light components from the liquid crystal display panels  39 ,  41  and  44  are directed through the beam splitters  38 ,  40  and  43  to a cross-prism  45  where they are combined. 
   After that, the R, G and B video image light components combined in the cross prism  45  are directed onto a projection lens  46  and then diffusion-projected onto a screen  47 . 
   Even with the projection display device equipped with such an optical system, by controlling the amount of light of each of the R, G and B light sources  30 ,  31  and  32  independently, the R, G and B luminance levels can be controlled as in the case of the previously described optical system. 
   The present invention is not limited to the above embodiment and may be practiced or embodied in still other ways without departing from the scope and spirit thereof.