Patent Publication Number: US-2015077715-A1

Title: Projector and method for compensating for amount of laser light

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims priority of Japanese Patent Application No. 2013-193309 filed on Sep. 18, 2013. The entire disclosure of the above-identified application, including the specification, drawings and claims is incorporated herein by reference in its entirety. 
     FIELD 
     The present invention relates to projectors, and, more particularly, to a projector which scans laser light onto a projection surface to project an image onto the projection surface. 
     BACKGROUND 
     Conventionally, projectors are known which scan laser light onto a projection surface, such as a screen or a wall, to project an image onto the projection surface. A projector has laser light sources having wavelengths of primary colors which are red, green, and blue, and emits the laser light having the wavelengths of the colors to project a color image onto a projection surface. 
     The laser light source is driven by a current and emits laser light that has an amount of light corresponding to the current. However, depending on environmental temperature surrounding the projector, an amount of laser light output from the laser light source varies even if the same magnitude of current is applied. 
     Thus, laser light control, known as APC (automatic power control) emission control, is performed. In APC emission control, a point, called a calibration point, is provided outside a region where an image is projected onto the projection surface, and laser light is constantly emitted at the calibration point. Thus, a bright point is projected near the projection surface, besides an image projected, and this is unsightly. 
     On the other hand, it is conceivable to block the laser light directed to the calibration point inside the projector. However, laser light blocking is difficult to achieve because the optical path of the laser light directed to the calibration point and the optical path of laser light for projecting an image are in close proximity. A projector which blocks laser light directed to a calibration point is also proposed (e.g., see PTL 1). 
     CITATION LIST 
     Patent Literature 
     [PTL 1] Japanese Unexamined Patent Application Publication No. 2009-141107 
     SUMMARY 
     Technical Problem 
     However, in the projector disclosed in PTL 1, a portion of the optical path of the laser light for image projection is encroached due to blocking of the optical path of the laser light directed to the calibration point. This causes a problem that image size is reduced. 
     The present invention is made to address the above problem and has an object to provide a projector which allows the APC emission control without use of a calibration point and without reducing image size. 
     Solution to Problem 
     To achieve the above object, a projector according to one aspect of the present invention is a projector including: a plurality of light source units configured to output laser light having wavelengths of different colors; a projection unit configured to scan the laser light output by the plurality of light source units over a projection surface to project an image onto the projection surface; a detection unit configured to detect a portion of amounts of the laser light output by the plurality of light source units for projecting the image; and a control unit configured to control the amounts of the laser light output by the plurality of light source units, based on color pixel values of each of pixels of the image, the color pixel values corresponding to the different colors, wherein the control unit is further configured to compensate for the amounts of the laser light, based on the portion of the amounts of the laser light detected by the detection unit, so that for each of the different colors, proportion of the amount of the laser light of the color output by one of the light source units to the color pixel value of the color in each of the pixels of the image which is projected onto the projection surface corresponds to predetermined proportion. 
     According to the above configuration, a portion of the amount of laser light that is used for image projection is used to compensate for the amount of laser light which are output from the light sources. This obviates the need for a calibration point in compensating for the amount of laser light. Thus, the APC emission control can be provided without use of a calibration point and without reducing image size. 
     Specifically, the control unit may include: a coefficient calculation unit configured to, using a first coefficient, calculate a second coefficient for each of the different colors, from the color pixel value of the color in each of the pixels of the image which is projected onto the projection surface and a portion of the amount of the laser light of the color detected by the detection unit when the laser light of the color is projected onto the pixel, the first coefficient indicating predetermined proportion of the amount of laser light of the color output by one of the light source units to the portion of the amount of laser light of the color which is output by the light source unit and detected by the detection unit, the second coefficient indicating proportion, to the color pixel value of the color, of the amount of the laser light of the color output by the light source unit based on the color pixel value; and a compensation unit configured to compensate for the amounts of the laser light output from the plurality of light source units so that the second coefficient calculated by the coefficient calculation unit for each of the different colors corresponds to a third coefficient indicating predetermined proportion of the amount of the laser light of the color output by one of the light source units to the color pixel value of the color. 
     Moreover, the coefficient calculation unit may randomly select the pixels in the image. 
     According to the above configuration, the pixels can be selected in a simple manner. 
     Moreover, the coefficient calculation unit may select, for each of the different colors, a pixel which has a maximum color pixel value of the color, as one of the pixels in the image. 
     According to the above configuration, a pixel that yields a largest amount of laser light can be selected for each color. Thus, the pixel is less susceptible to noise, as compared with selection of a pixel that yields a small amount of laser light, and therefore the second coefficients can be accurately obtained. 
     Moreover, the coefficient calculation unit may select, as the pixels in the image, a pixel that has a largest sum of the color pixel values of the different colors, and, from among pixels each having the color pixel values of 0 or greater, a pixel that has a smallest sum of the color pixel values and a pixel that has a medium sum of the color pixel values. 
     According to the above configuration, pixels that yield various amounts of light can be selected. Thus, the second coefficients can be accurately obtained, as compared with use of pixels that yield a similar amount of laser light. 
     Moreover, the coefficient calculation unit may calculate the second coefficient, when the color pixel values of each of the pixels are greater than 0. 
     If an amount of laser light of any color is 0, the simultaneous equations using the first coefficients and the second coefficients cannot be solved. However, according to the above configuration, such a case is excluded, thereby accurately obtaining the second coefficients. 
     Moreover, the projection unit may include: a mixer unit configured to mix the laser light output from the plurality of light source units to output mixed light; a beam splitter which divides the mixed light into two beams; and a mirror which causes one of the two beams obtained by the beam splitter to be scanned onto the projection surface, and the detection unit may detect an amount of light of the other of the two beams obtained by the beam splitter as the portion of the amounts of the laser light output by the plurality of light source units. 
     According to the above configuration, the portion of the amount of laser light can be directed to the detection unit in a simple configuration. 
     It should be noted that the present invention can be implemented not only as a projector that includes such characteristic processing units but also as a method for compensating for an amount of laser light, which includes, as steps, processes which are performed by the characteristic processing units included in the projector. The present invention can also be implemented as a program for causing a computer to function as the characteristic processing units included in the projector, or a program for causing a computer to execute the characteristic steps included in the method for compensating for an amount of laser light. In addition, such a program can, of course, be distributed in a non-transitory computer-readable storage medium such as a compact disc read only memory (CD-ROM) and via a communication network such as the Internet. 
     Advantageous Effects 
     According to the present invention, APC emission control without use of a calibration point and without reducing image size can be provided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the present invention. 
         FIG. 1  is a block diagram of a hardware configuration of a projector according to an embodiment 1. 
         FIG. 2  is a flowchart illustrating a process of compensating for an amount of laser light by the projector according to the embodiment 1. 
         FIG. 3  is a flowchart illustrating a process of compensating for an amount of laser light by a projector according to an embodiment 2 
         FIG. 4  is a flowchart illustrating a process of compensating for an amount of laser light by a projector according to an embodiment 3. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments according to the present invention will be described, with reference to the accompanying drawings. It should be noted that the embodiments described below are each merely a preferred illustration of the present invention. Values, shapes, materials, components, arrangement or connection between the components, steps, and the order of the steps are merely illustrative, and are not intended to limit the present invention. The present invention is indicated by the appended claims. Thus, among components of the embodiments below, components not set forth in the independent claims are not necessary to achieve the present invention but will be described as components for preferable embodiments. 
     Embodiment 1 
     1. Configuration 
       FIG. 1  is a block diagram of a hardware configuration of a projector according to an embodiment 1. 
     A projector  10  scans laser light  121  over a projection surface  108  to project an image onto the projection surface  108 . The projector  10  includes a red light source unit  101 R, a green light source unit  101 G, a blue light source unit  101 B, a projection unit  130 , an optical electrical integrated circuit (OEIC)  104 , and a control unit  107 . 
     The red light source unit  101 R is a laser diode which outputs laser light  120 R having a red wavelength. 
     The green light source unit  101 G is a laser diode which outputs laser light  120 G having a green wavelength. 
     The blue light source unit  101 B is a laser diode which outputs laser light  120 B having a blue wavelength. 
     The projection unit  130  scans, over the projection surface  108 , three laser light beams  120 R,  120 G, and  120 B which are respectively output from the red light source unit  101 R, the green light source unit  101 G, and the blue light source unit  101 B to project an image onto the projection surface  108 . The projection unit  130  includes a mixer unit  102 , a beam splitter  103 , a lens  105 , and a mirror  106 . 
     The mixer unit  102  mixes the three laser light beams  120 R,  120 G, and  120 B which are respectively output from the red light source unit  101 R, the green light source unit  101 G, and the blue light source unit  101 B, and outputs laser light  120 . The mixer unit  102  is configured with a dichroic prism, for example. 
     The beam splitter  103  is, for example, configured with a half mirror, and divides the laser light  120  into the laser light  121  and laser light  122 . 
     The lens  105  condenses the laser light  121  that has passed through the beam splitter  103 . 
     The mirror  106  is, for example, a MEMS (micro electro mechanical systems) mirror, and oscillated in the horizontal direction (x direction) and the vertical direction (y direction) to reflect the laser light  121  which has passed through the lens  105 . The mirror  106  causes the laser light  121  to be scanned over the projection surface  108  to project an image onto the projection surface  108 . 
     The OEIC  104  (included in a detection unit) detects an amount of the laser light  122  output from the beam splitter  103 . 
     The control unit  107  supplies drive currents to the red light source unit  101 R, the green light source unit  101 G, and the blue light source unit  101 B, and adjusts an amount of the laser light from each light source unit by adjusting the supplied drive current. The control unit  107  further compensates for the amounts of the laser light, based on the portion of the amounts of the laser light detected by the OEIC  104 , so that for each of the different colors, proportion of the amount of the laser light of the color output by one of the light source units to the color pixel value of the color in each of the pixels of the image which is projected onto the projection surface  108  corresponds to predetermined proportion. The control unit  107  controls driving of the mirror  106 . The control unit  107  is configured with a computer system which includes a processor and a memory. 
     The memory functions as an initial coefficient storage unit  112 . 
     The control unit  107  includes a coefficient calculation unit  111  and a compensation unit  113  as functional processing units which are implemented by execution, on a processor, of a program for compensating for the amount of laser light. 
     The initial coefficient storage unit  112  stores first coefficients and third coefficients. The first coefficient indicates predetermined proportion of the amount of laser light of a color output by one of the light source units to the portion of the amount of laser light of the color which is output by the light source unit and detected by the OEIC  104 . The third coefficient indicates predetermined proportion of the amount of the laser light of a color output by one of the light source units to the color pixel value of the color. 
     The first coefficients and the third coefficients will be described below. The first coefficients and the third coefficients are determined and adjusted in manufacturing the projector  10 . 
     Table 1 illustrates the first coefficients. The first coefficients are obtained by the equations: α=R0/Ro0, β=G0/Go0, and γ=B0/Bo0, respectively, where Ro0, Go0, and Bo0 indicate amounts of the laser light  122  having red, green, and blue wavelengths, respectively, which are detected by the OEIC  104 , R0, G0, and B0 indicate amounts of output of the laser light  120 R,  120 G, and  120 B, respectively, from which the laser light  122  originates, and α, β, and γ indicate the first coefficients for red, green, and blue, respectively. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Detected 
                 Amount of 
                   
               
               
                   
                 Color 
                 amount of light 
                 output of light 
                 First coefficient 
               
               
                   
                   
               
             
            
               
                   
                 Red 
                 Ro0 
                 R0 
                 α = R0/Ro0  
               
               
                   
                 Green 
                 Go0 
                 G0 
                 β = G0/Go0 
               
               
                   
                 Blue 
                 Bo0 
                 B0 
                 γ = B0/Bo0 
               
               
                   
                   
               
            
           
         
       
     
     Table 2 illustrates the third coefficients. The third coefficients are obtained by the equations: Rt0=R0/r0, Gt0=G0/g0, Bt0=B0/b0, respectively, where r0, g0, and b0 indicate a red pixel value, a green pixel value, and a blue pixel value, respectively, and Rt0, Gt0, and Bt0 indicate the third coefficients for red, green, and blue, respectively. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                   
                 Amount of 
                   
               
               
                   
                 Color 
                 Pixel value 
                 output of light 
                 Third coefficient 
               
               
                   
                   
               
             
            
               
                   
                 Red 
                 r0 
                 R0 
                 Rt0 = R0/r0     
               
               
                   
                 Green 
                 g0 
                 G0 
                 Gt0 = G0/g0 
               
               
                   
                 Blue 
                 b0 
                 B0 
                 Bt0 = B0/b0 
               
               
                   
                   
               
            
           
         
       
     
     The coefficient calculation unit  111 , using a first coefficient, calculates a second coefficient for each color, from the color pixel value of the color in each of the pixels of the image which is projected onto the projection surface  108  and an amount of the laser light of the color detected by the OEIC  104  when the laser light of the color is projected onto the pixel. The second coefficient indicates proportion, to the color pixel value of the color, of the amount of the laser light of the color output by the light source unit based on the color pixel value. A method of calculating the second coefficient will be described below. 
     The compensation unit  113  compensates for amounts of the laser light output from the plurality of light source units so that the second coefficient calculated by the coefficient calculation unit  111  for each color corresponds to the third coefficient for the color. 
     2. Processing 
     Next, a process, by the projector  10 , of compensating for the amounts of laser light from the red light source unit  101 R, the green light source unit  101 G, and the blue light source unit  101 B will be described. The process of compensating for the amounts of laser light is performed each time one image is projected onto the projection surface  108 , namely, frame by frame. 
       FIG. 2  is a flowchart illustrating the process, by the projector  10  according to the embodiment 1, of compensating for an amount of laser light. 
     The coefficient calculation unit  111  sets a counter n to 1 (S 1 ). The counter n is a variable stored in the memory. 
     The coefficient calculation unit  111  randomly selects one pixel in the image which is projected onto the projection surface  108  (S 2 ). 
     The coefficient calculation unit  111  obtains, from the OEIC  104 , an amount of the laser light  122  that is detected by the OEIC  104  when the laser light  121  is projected onto the selected pixel (S 3 ). 
     The coefficient calculation unit  111  obtains color pixel values of the selected pixel (S 4 ). Color pixel values of pixels are previously stored in the memory. The pixels each include color pixel values each represented by, for example, an 8-bit value in a range from 0 to 255, indicating a red pixel value, a green pixel value, or a blue pixel value. 
     The coefficient calculation unit  111  determines whether any of the color pixel values is 0 (S 5 ). 
     If none of the color pixel values is 0 (NO in S 5 ), the coefficient calculation unit  111  increments the counter n by 1 (S 6 ). 
     The coefficient calculation unit  111  determines whether the counter n is 4 (S 7 ). 
     If the counter n is less than 4 (NO in S 7 ), the processing returns to S 2 . If the counter n is 4 (YES in S 7 ), this indicates that the amounts of the laser light  122  and pixel values for three pixels in the image have been obtained through the foregoing processing. 
     The coefficient calculation unit  111  uses the obtained amounts of the laser light  122  and pixel values to calculate the second coefficients (S 8 ). Details of the method of calculating the second coefficient will be descried below. 
     The following simultaneous equations (Eq. 1) stand: 
     
       
         
           
             
               
                 
                   
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     where An (n=1, 2, 3) indicates the amounts of the laser light  122  obtained in S 3 , rn, gn, and bn (n=1, 2, 3) indicate a red pixel value, a green pixel value, and a blue pixel value, respectively, obtained in S 4 , and Rt, Gt, and Bt indicate the second coefficients for red, green, and blue, respectively. 
     The coefficient calculation unit  111  solves the simultaneous equations indicated in Eq. 1 to calculate the second coefficients Rt, Gt, and Bt. 
     The compensation unit  113  compares the second coefficients calculated by the coefficient calculation unit  111  and the corresponding third coefficients to compensate for the drive currents to be supplied to the red light source unit  101 R, the green light source unit  101 G, and the blue light source unit  101 B so that values of the second coefficients correspond to values of the corresponding third coefficients, thereby compensating for the amount of laser light to be output from each light source unit (S 9 ). It should be noted that the image projection onto the projection surface  108  may be ended at the end of the second coefficient calculation process (S 8 ). Thus, the compensation process (S 9 ) may be performed on a frame that follows the frame undergone the second coefficient calculation process (S 8 ). 
     If any of the color pixel values obtained in the process of S 4  is 0 (YES in S 5 ), the compensation unit  113  compensates for the same amount of laser light for the frame as with the previous frame (S 10 ). 
     3. Effect 
     As described above, according to the embodiment 1, using an amount of a portion of the laser light used for image projection, the compensation unit  113  compensates for the amount of laser light. This compensates for the amount of laser light, without a calibration point. Thus, APC emission control can be provided without use of a calibration point and without reducing the image size. 
     The three pixels are randomly selected from the image, allowing the pixel selection in a simple manner. 
     If an amount of laser light of any color is 0, the simultaneous equations indicated in Eq. 1 cannot be solved. In the above process, however, such a case is excluded, thereby accurately obtaining the second coefficients. 
     Embodiment 2 
     Next, a projector according to an embodiment 2 will be described. The embodiment 2 is different from the embodiment 1 in method of selecting a pixel in an image. 
     The projector according to the embodiment 2 has the same configuration as the projector  10  according to the embodiment 1 as shown in  FIG. 1 . Thus, the detailed description will not be repeated herein. 
       FIG. 3  is a flowchart illustrating a process of compensating for an amount of laser light by the projector  10  according to the embodiment 2. 
     The coefficient calculation unit  111  selects one pixel that has a maximum red pixel value in the image which is projected onto the projection surface  108  (S 11 ). 
     The coefficient calculation unit  111 , as with the processes of S 3  and S 4  in  FIG. 2 , obtains an amount of the laser light  122  detected by the OEIC  104  for the selected pixel (S 12 ), and obtains a pixel value of the selected pixel (S 13 ). 
     The coefficient calculation unit  111  determines whether any of the color pixel values of the pixel is 0 (S 14 ) 
     If none of the color pixel values is 0 (NO in S 14 ), the same processes as the processes of S 11  to S 14  are repeated for the cases of a maximum green pixel value and a maximum blue pixel value (S 15  to S 22 ). The amounts of the laser light  122  and the pixel values are obtained through the foregoing processing, with respect to a pixel having a maximum red pixel value, a pixel having a maximum green pixel value, and a pixel having a maximum blue pixel value. 
     The coefficient calculation unit  111  uses the obtained amounts of the laser light  122  and pixel values to calculate the second coefficients (S 8 ), and the compensation unit  113  compensates for the amount of laser light output from the light source unit of each color (S 9 ). The processes of S 8  and S 9  are as described in the embodiment 1. Thus, the detailed description will not be repeated herein. 
     If any of the color pixel values obtained in the process of S 13 , S 17 , and S 21  is 0 (YES in S 14 , YES in S 18 , or YES in S 22 ), the compensation unit  113  compensates for the same amount of laser light for the frame as with the previous frame (S 10 ). 
     As described above, according to the embodiment 2, a pixel that yields a largest amount of laser light can be selected for each color. Thus, the pixel is less susceptible to noise, as compared with selection of a pixel that yields a small amount of laser light, and therefore the second coefficients can be accurately obtained. 
     Embodiment 3 
     Next, a projector according to an embodiment 3 will be described. The embodiment 3 is different from the embodiment 1 in method of selecting a pixel in an image. 
     The projector according to the embodiment 3 has the same configuration as the projector  10  according to the embodiment 1 as shown in  FIG. 1 . Thus, the detailed description will not be repeated herein. 
       FIG. 4  is a flowchart illustrating a process of compensating for an amount of laser light by a projector  10  according to the embodiment 3. 
     In the image which is projected onto the projection surface  108 , the coefficient calculation unit  111  selects pixels which has a maximum sum of red, green, and blue pixel values from among pixels in which none of red, green, and blue pixel values is 0 (S 31 ). 
     The coefficient calculation unit  111 , as with the processes of S 3  and S 4  in  FIG. 2 , obtains an amount of the laser light  122  detected by the OEIC  104  for the selected pixel (S 32 ), and obtains a pixel value of the selected pixel (S 33 ). 
     Next, in the image which is projected onto the projection surface  108 , the coefficient calculation unit  111  selects a pixel which has a minimum sum of red, green, and blue pixel values from among pixels in which none of red, green, and blue pixel values is 0 (S 34 ). 
     The coefficient calculation unit  111 , as with the processes of S 3  and S 4  in  FIG. 2 , obtains an amount of the laser light  122  detected by the OEIC  104  for the selected pixel (S 35 ), and obtains a pixel value of the selected pixel (S 36 ). 
     Next, in the image which is projected onto the projection surface  108 , the coefficient calculation unit  111  selects a pixel which has a medium sum of red, green, and blue pixel values from among the pixels in which none of red, green, and blue pixel values is 0 (S 37 ). 
     The coefficient calculation unit  111 , as with the processes of S 3  and S 4  in  FIG. 2 , obtains an amount of the laser light  122  detected by the OEIC  104  for the selected pixel (S 38 ), and obtains a pixel value of the selected pixel (S 39 ). 
     The amounts of the laser light  122  and the pixel values are obtained through the foregoing processing, with respect to a pixel which has a maximum sum of red, green, and blue pixel values, a pixel which has a minimum sum of red, green, and blue pixel values, and a pixel which has a medium sum of red, green, and blue pixel values. 
     The coefficient calculation unit  111  uses the obtained amounts of the laser light  122  and pixel values to calculate the second coefficients (S 8 ), and the compensation unit  113  compensates for the amount of laser light to be output from the light source unit of each color (S 9 ). The processes of S 8  and S 9  are as described in the embodiment 1. Thus, the detailed description will not be repeated herein. 
     As described above, according to the embodiment 3, pixels that yield various amounts of light can be selected. Thus, the second coefficients can be accurately obtained, as compared with use of pixels that yield a similar amount of laser light. 
     The projector according to the embodiments of the present invention has been described above. The present invention, however, is not limited to the embodiments described above. 
     For example, in the above-described embodiment, three pixels are selected in an image to calculate the second coefficients. However, the number of pixels selected in the image is not limited to three. For example, four or more pixels may be selected and four or more equations similar to those indicated in Eq. 1 may be produced based on values obtained from the pixels to calculate the second coefficients from the equations by least squares. 
     Moreover, the control unit  107  described above may be configured in, specifically, a computer system which includes a microprocessor, a read only memory (ROM), a random access memory (RAM), a hard disk drive, a display unit, a keyboard, a mouse, and so on. A computer program is stored in the RAM or the hard disk drive. The function of the control unit  107  is performed by the microprocessor operating according to the computer program. Here, the computer program includes a combination of a plurality of instruction codes for giving instructions to the computer to perform predetermined functions. 
     Furthermore, some or the whole of the components included in the control unit  107  described above may be configured with one system large scale integration (LSI). The system LSI is a super multi-function LSI fabricated by integrating a plurality of components on one chip, and is, specifically, a computer system which includes a microprocessor, a ROM, a RAM, and so on. A computer program is stored in the RAM. The system LSI performs its functionality by the microprocessor operating according to the computer program. 
     Furthermore, some or the whole of the components included in the control unit  107  described above may be configured with an IC card or a single module detachable to the projector  10 . The IC card or the module is a computer system which includes a microprocessor, a ROM, a RAM, and so on. The IC card or the module may include the super multi-function LSI described above. The IC card or the module performs its functionality by the microprocessor operating according to the computer program. The IC card or the module may be of tamper-resistant. 
     Moreover, the present invention may be implemented in the above-described method for compensating for an amount of laser light. Moreover, the present invention may be achieved in a computer program implementing such a method via a computer, or may be implemented in a digital signal that comprises the computer program. 
     Furthermore, the present invention may be achieved in a non-transitory computer-readable recording medium having stored therein the computer program or the digital signal, such as a flexible disk, a hard disk, CD-ROM, MO, DVD, DVD-ROM, DVD-RAM, BD (Blu-ray (registered trademark) Disc), and a semiconductor memory. Moreover, the present invention may be implemented in the digital signal stored in such a non-transitory recording medium. 
     Moreover, the present invention may be achieved in transmitting the computer program or the digital signal via an electric communication line, a wireless or wired communication line, a network represented by the Internet, data broadcast, or the like. 
     Moreover, the present invention may be achieved in a computer system which includes a microprocessor and a memory. The memory may store the computer program and the microprocessor may operate according to the computer program. 
     Moreover, by transferring the program or the digital signal in the non-transitory recording medium or transferring the program or the digital signal via the network or the like, the program or the digital signal may be executed in another independent computer system. 
     Furthermore, the above-described embodiments may be combined. 
     Although only some exemplary embodiments of the present invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of the present invention. Accordingly, all such modifications are intended to be included within the scope of the present invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention is, as a projector, applicable to on-board head-up displays in automobiles, for example.