Abstract:
A projection display apparatus includes: a display element that displays an image; a lamp that illuminates the display element to cause the display element to emit an image light; a variable light intensity element that allows the light emitted from the lamp to pass therethrough, the intensity of light passing through the variable light intensity element being variable; and a light intensity controller that determines whether the display element is at an image mute state in which a full-black image is displayed, or at a normal lighting state other than the image mute state, and when the display element is at the image mute state, reduces the amount of power supplied to the lamp to a level that is lower than that of the normal lighting state to decrease the intensity of light emitted from the lamp, and also decreases the intensity of light that passes through the variable light intensity element.

Description:
TECHNICAL FIELD 
     The present invention relates to a projection display apparatus and control method therefor. 
     BACKGROUND ART 
     When a projection display apparatus is projecting an image light onto a screen, the projection may be temporarily interrupted according to operation which is entered by a user. A projection display apparatus has been discussed in which the amount of lamp power that is supplied to a lamp is reduced in order to conserve electrical power during periods when the projection is interrupted. The configuration of such a projection display apparatus is illustrated in  FIG. 1 . 
     The projection display apparatus illustrated in  FIG. 1  comprises power source  11 , ballast  12 , lamp  13 , image signal controller  14 , display element  15 , and light intensity controller  16 . In  FIG. 1 , an outline arrow indicates a light flux. 
     Ballast  12  adjusts the lamp power that is supplied from power source  11  to lamp  13  in accordance with a control signal received from light intensity controller  16 . Lamp  13  is lighted by a lamp power supplied from power source  11  via ballast, and illuminates display element  15 . 
     Image signal controller  14  receives an image signal from the outside and provides the image signal to display element  15 . Display element  15  displays an image indicated by the image signal received from image signal controller  14 . Display element  15  may be, for example, a liquid crystal element that is sandwiched by deflection plates in the form of crossed Nichol prism. 
     By being illuminated by the light emitted from lamp  13 , an image light emitted from display element  15  is projected onto screen  20 . 
     Light intensity controller  16  receives an interrupt operation to interrupt projection which is entered by the user. When the interrupt operation is entered, light intensity controller  16  instructs image signal controller  14  to cause display element  15  to display a full-black image. By performing a control to display a full-black image on display element  15 , light emitted from lamp  13  is unable to reach screen  20 , thus interrupting the projection. In the following, a state in which projection is interrupted is called “an image mute state”, and a state other than the image mute state is called “a normal lighting state”. 
     When the interrupt operation is entered, light intensity controller  16  also provides a control signal to ballast  12  such that lamp power that is lower than lamp power at the normal lighting state is supplied to lamp  12 . 
     Projection display apparatus  10  described above achieves power saving because during the interruption of projection, low-power lighting is performed in which lamp  13  is lighted up with lamp power whose level is lower than the level during a normal lighting state. 
     Typically, a lamp of a projection display apparatus is a discharge lamp. Accordingly, lighting a lamp at a lamp power that is lower than a predetermined power (rated power) causes unstable light emission and damages the electrode and luminous tube of the lamp. 
     Thus, Patent Document 1 (JP2009-093862A) discloses a technique in which, if the lamp power is lower than the rated power for a certain period of time or longer, then a lamp refreshing process is carried out to temporarily increase the lamp power at the appropriate time interval. According to this technique, even if lighting a lamp at a lamp power that is lower than the rated power damages the electrode and the luminous tube of the lamp, the lamp refreshing process can return the states of the electrode and the luminous tube to normal states. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1 JP2009-093862A SUMMARY OF INVENTION 
     Problems to Be Solved By the Invention 
     However, the above-described projection display apparatus is problematic in that only by displaying a full-black image onto display element  15 , it is impossible to completely interrupt light emitted from lamp  13 , and a certain light intensity reaches screen  20 , thus causing image light that is difficult to see, be projected. 
     Furthermore, in the case of applying the technique disclosed in Patent Document 1 to projection display apparatus  10 , the lamp refreshing process causes the lamp power to vary at a timing that is not intended by the user. Variation in lamp power, in turn, varies the luminance of lamp  13 . This variation causes a problem of variation in brightness of the image light. 
     It is an object of the present invention to provide a projection display apparatus and a control method therefor that can solve the problem described above. 
     Means to Solve the Problems 
     To achieve the above-described object, a projection display apparatus according to the present invention that projects an image light based on an image, comprises: 
     a display element that displays said image; 
     a lamp that illuminates the display element to cause the display element to emit the image light; 
     a variable light intensity element that allows the light emitted from the lamp to pass therethrough, the intensity of light passing through the variable light intensity element being variable; and 
     a light intensity controller that determines whether the display element is at an image mute state in which a full-black image is displayed, or at a normal lighting state other than the image mute state, and when the display element is at the image mute state, reduces the amount of power supplied to the lamp to a level that is lower than that of the normal lighting state to decrease the intensity of light emitted from the lamp, and also decreases the intensity of light that passes through the variable light intensity element 
     To achieve the above-described object, a control method in a projection display apparatus according to the present invention comprises: a display element that displays an image; a lamp that illuminates the display element to cause the display element to emit an image light; a variable light intensity element that allows the light emitted from the lamp to pass therethrough, the intensity of light passing through the variable light intensity element being variable, 
     wherein a light intensity controller determines whether the display element is at an image mute state in which a full-black image is displayed, or at a normal lighting state other than the image mute state, and when the display element is at the image mute state, reduces the amount of power supplied to the lamp to a level that is lower than that of the normal lighting state to decrease the intensity of light emitted from the lamp, and also decreases the intensity of light that passes through the variable light intensity element. 
     Effects of the Invention 
     According to the present invention, when a projection display apparatus detects that the display element is at the image mute state, the projection display apparatus reduces the amount of power supplied to the lamp to a level that is lower than that of the normal lighting state to decrease the intensity of light emitted from the lamp, and also decreases the intensity of light that passes through the variable light intensity element. This makes it possible to prevent variation in brightness of image light on the screen due to variation in lamp power. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing the configuration of a related projection display apparatus. 
         FIG. 2  is a block diagram showing the configuration of a projection display apparatus according to an exemplary embodiment of the present invention. 
         FIG. 3  is a view explaining the operation of the projection display apparatus shown in  FIG. 2 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Exemplary embodiments of the present invention will be described below with reference to the drawings. 
       FIG. 2  is a block diagram showing the configuration of projection display apparatus  100  according to an exemplary embodiment of the present invention. Note that the same components as those in  FIG. 2  as those in  FIG. 1  are denoted by the same reference numerals and that a description thereof will be omitted. In  FIG. 2 , an outline arrow indicates a light flux. 
     Projection display apparatus  100  shown in  FIG. 2  comprises power source  11 , ballast  12 , lamp  13 , image signal controller  14 , display element  15 , variable light intensity element  101  and light intensity controller  102 . 
     Variable light intensity element  101  is an element which is provided between lamp  13  and display element  15 , and which allows the light emitted from lamp  13  to pass therethrough, the intensity of light passing through the variable light intensity element being variable. In the following explanation, an aperture will be used as an example of variable light intensity element  101 . Variable light intensity element  101  adjusts the opening of the aperture in accordance with a control signal output from light intensity controller  102 . 
     Light intensity controller  102  is adapted to receive an interrupt operation which is entered by the user. When the interrupt operation is entered, light intensity controller  102  instructs image signal controller  14  to cause display element  15  to display a full-black image. Light intensity controller  102  also receives a resume operation which is entered after the entry of the interrupt operation, to resume projection. When the resume operation is entered, light intensity controller  102  instructs image signal controller  14  to cause display element  15  to display an image indicated by the image signal. 
     During the period from the entry of the interrupt operation to the entry of the resume operation, light intensity controller  102  detects that display element  15  is in the image mute state, and provides a control signal to ballast  12  to decrease the lamp power supplied from power source  11  to lamp  13  from the power at the normal lighting state. 
     When display element  15  enters the image mute state, light intensity controller  102  provides a control signal to variable light intensity element  101  to change the opening of the aperture which is variable light intensity element  101 . 
     Next, an operation of projection display apparatus  100  will be described with reference to  FIG. 3 . 
       FIG. 3(   a ) is a timing chart of the lamp power,  FIG. 3(   b ) is a timing chart of the opening of the aperture which is variable light intensity element  101 , and  FIG. 3(   c ) is a timing chart of the brightness on the screen when projection is interrupted during the implementation of projection by projection display apparatus  10  shown in  FIG. 1  and by projection display apparatus  100  according to the present exemplary embodiment. In  FIG. 3(   c ), a solid line, and a dotted line show the brightness on the screen when the projection is interrupted during the implementation of projection by projection display apparatus  10  and projection display apparatus  100 , respectively. 
     When the projection is started, light intensity controller  102  receives an interrupt operation which is entered by the user. 
     When the interrupt operation is entered at time t 1 , light intensity controller  102  instructs image signal controller  14  to cause display element  15  to display a full-black image. When display element  15  transitions to the image mute state in which the full-black image is displayed, the brightness on the screen decreases as shown in  FIG. 3(   c ). 
     When display element  15  enters the image mute state at time t 1 , light intensity controller  102  provides a control signal to ballast  12  to cause a smaller amount of power to be supplied to lamp  13  that the amount of power that is supplied at the normal lighting state. As shown in  FIG. 3(   a ), in response to the control signal received from light intensity controller  102 , ballast  12  adjusts the lamp power supplied from power source  11  to lamp  13  such that the amount of power that is supplied to lamp  13  is smaller than the amount of power that is supplied at the normal lighting state. As a result, lamp  13  is lighted by using the low power of lamp power a, which decreases the intensity of the light emitted from lamp  13 . 
     Here, lamp power a is set at a power which is equal to or less than 30% of lamp power at the normal lighting state, for example. If lamp  13  is turned off when projection is interrupted, it takes much time for lamp  13  to be lighted again when it returns to the normal lighting state, etc. However, if lamp  13  is not turned of and is lighted by using low power, then the amount of time that is needed for brightness to be restored to lamp  13 , when it returns to the normal lighting state, is shortened. In the following, it is assumed that lamp power a is lower than the rated power of lamp  13 . 
     When display element  15  enters the image mute state at time t 1 , light intensity controller  102  provides a control signal to variable light intensity element  101  to make the opening of the aperture smaller than that at the normal lighting state. As shown in  FIG. 3(   b ), in response to the control signal received from light intensity controller  102 , variable light intensity element  101  makes the opening of the aperture smaller than that at the normal lighting state. As a result, the intensity of the light emitted from lamp  13  that passes through the aperture is decreased. 
     Next, light intensity controller  102  measures the elapsed time after the start of low power lighting. 
     As described earlier, if lamp  13  is lighted by using an amount of power that is smaller than the rated power, then the emission of light becomes unstable, causing damages to the electrodes and luminous tubes. 
     Hence, in order to restore the electrodes and luminous tubes of lamp  13  to the normal state when a predetermined time has elapsed since the low power lighting started, light intensity controller  102  performs a lamp refreshing process to temporarily increase the lamp power at a suitable time interval. 
     In the following, assume that as the lamp refreshing process is executed, light intensity controller  102  performs an operation to provide a control signal to ballast  12  such that when the low power lighting is continued for 30 minutes, lamp power b, which is 70% of the lamp power at the normal lighting state, is supplied to lamp  13  for 10 minutes, and then original lamp power a is supplied to lamp  13 . 
     As shown in  FIG. 3(   a ), in response to the control signal received from light intensity controller  102 , ballast  12  makes an adjustment such that lamp power b is supplied to lamp  13  between time t 2  that is 30 minutes after t 1 , and time t 3  that is 10 minutes after t 2 , and lamp power a is supplied to lamp  13  after time t 3 . Please note that the opening of the aperture remains small even during the execution of the lamp refreshing process. 
     As describe above, projection display apparatus  10  suffers from two problems as described below. 
     The first problem is that only causing display element to display a full-black image results in the projection of image light onto screen  20  that is difficult to see. 
     The second problem is that the lamp refreshing process may cause the lamp power to increase at timings that are not intended by the user, thus changing the brightness on screen  20 . 
     In contrast, according to projection display apparatus  100  of the present exemplary embodiment, the intensity of the light emitted from lamp  13  that passes through variable light intensity element  101  is decreased, thereby ensuring that light emitted from lamp  13  is interrupted. 
     Accordingly, as shown  FIG. 3(   c ), at the low-power lighting after time t 1 , projection display apparatus  100  can cause the brightness on screen  20  to be lower than the brightness that is projected onto screen  20  by projection display apparatus  10 , and furthermore can prevent the variation of the brightness on screen  20  during a time period between t 2  and t 3  of which the lamp refreshing process is performed. 
     The present exemplary embodiment illustrates, as an example, that lamp  13 , variable light intensity element  101 , and display element  15  are arranged along the light path in this order, but the arrangement of these elements is not limited thereto. For example, lamp  13 , display element  15 , and variable light intensity element  101  may be arranged along the light path in this order. 
     The present exemplary embodiment illustrates, as an example, that as variable light intensity element  101 , an aperture is used, but variable light intensity element  101  is not limited thereto. For example, a permeable liquid crystal element may be used as variable light intensity element  101 . Alternatively, a shutter may be used to completely shut off light. 
     When an aperture is used as variable light intensity element  101 , the diameter of the beam of light emitted from the lamp may undergo a change. However, use of crystal liquid element can inhibit a change in the diameter of the beam of light. 
     Now consider a case in which the intensity of the light from the lamp is constant. When a liquid crystal element is used as variable light intensity element  101 , even if a control to make constant the intensity of the light that passes through the liquid crystal element is performed, the intensity may be changed. However, this will not occur when an aperture is used, and light emitted from lamp  13  is reliably interrupted. 
     The present exemplary embodiment illustrates, as an example, that when an interrupt operation is entered, light intensity controller  102  performs a control to decrease the lamp power at the same timing as a timing at which a full-black image is displayed onto display element  15 . However, the timing at which the lamp power is decreased, is not limited thereto, and may differ from a timing at which the full-black image is displayed onto display element  15 . Alternatively, for example, light intensity controller  102  may determine whether or not an image signal has been entered, and when it is determined that the image signal has not been entered, may automatically decrease the lamp power, 
     Furthermore, the present exemplary embodiment illustrates, as an example, that when an interrupt operation is entered, the intensity of light that passes through variable light intensity element  101  is decreased at the same timing as the timing at which the lamp power is decreased. However, the timing at which the intensity of light that passes through variable light intensity element  101 , is decreased, is not limited thereto. In order to prevent the change of the brightness on screen  20 , the intensity of light that passes through variable light intensity element  101  may be decreased at an arbitrary timing prior to the lamp refreshing process. 
     The invention of this application has thus been described with reference to exemplary embodiments. However, the present invention is not limited to the exemplary embodiments. Various modifications that those skilled in the art can understand may be made in configurations or details of the invention of this application within the scope of the invention of this application.