Patent Publication Number: US-2011069235-A1

Title: Excellently Operable Projection Image Display Apparatus

Description:
This nonprovisional application is based on Japanese Patent Application No. 2009-216596 filed on Sep. 18, 2009, with the Japan Patent Office, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to projection image display apparatuses and particularly to projection image display apparatuses having a function correcting a distortion of an image displayed on a projection surface. 
     2. Description of the Related Art 
     Projection image display apparatuses (hereinafter also referred to as projectors) may cause a so called image distortion. More specifically, between the optical axis of light projected by a projector and a screen or a similar projection surface, there may be a relative inclination, and accordingly, an image projected on the projection surface may distort at least in one of horizontal and vertical directions. 
     Normally, projectors are provided with a correction function for correcting such image distortion. For example, a projector has been studied that has a first trapezoid correction key operated to correct a projected image&#39;s trapezoidal distortion in a predetermined direction, and a second trapezoid correction key operated to correct the projected image&#39;s trapezoidal distortion in a direction opposite to that associated with the first trapezoid correction key. The projector is operated by a user operating the keys to correct image distortion. 
     In operating this projector by operating the keys to correct image distortion if an image signal is not sharp it is difficult for the user to visually observe how an image projected and thus displayed on a screen is distorted, resulting in poorly operable image distortion correction. 
     SUMMARY OF THE INVENTION 
     The present invention contemplates a projection image display apparatus with an image distortion correction function that is improved in operability in correcting image distortion. 
     The present invention in one aspect provides a projection image display apparatus including: an image signal processing unit which receives and converts a first image signal to generate a second image signal representing an image to be projected; an image distortion correction unit which corrects the second image signal in response to a correction point on a projected image being changed by an operation done by a user; and a distortion correction screen generation unit which operates, when an image distortion correction process is selected in response to an operation done by the user, to superpose on the projected image a correction pattern used to allow the user to designate the correction point, and thus display the correction pattern and the projected image on a single screen. The distortion correction screen generation unit includes a switching control unit which switches a color used to display the correction pattern when the image distortion correction process is performed. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows a configuration of a projection image display apparatus according to a first embodiment of the present invention. 
         FIG. 2  shows a configuration of a projector shown in  FIG. 1 . 
         FIG. 3  illustrates a remote controller shown in  FIG. 1 . 
         FIG. 4  illustrates an image distortion correction image. 
         FIG. 5  illustrates an image distortion correction process according to the first embodiment. 
         FIG. 6  is a flowchart for illustrating a process according to the first embodiment for controlling how a color that is displayed is switched. 
         FIG. 7  illustrates designating a color by a user for a correction pattern. 
         FIG. 8  illustrates a process according to a second embodiment for controlling how a color used to display a correction pattern is switched. 
         FIG. 9  is a flowchart for illustrating a process according to the second embodiment for controlling how a color that is displayed is switched. 
         FIG. 10  is a flowchart for illustrating a process according to the second embodiment in an exemplary variation for controlling how a color that is displayed is switched. 
         FIG. 11  is a flowchart for illustrating a process according to a third embodiment for controlling how a color that is displayed is switched. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter reference will be made to the drawings to describe the present invention in embodiments. In the figures, identical or corresponding components are identically denoted and will not be described repeatedly in detail, 
     First Embodiment 
       FIG. 1  schematically shows a configuration of a projection image display apparatus according to a first embodiment of the present invention. 
     With reference to  FIG. 1 , the first embodiment provides a projection image display apparatus (hereinafter also referred to as a projector)  10  that is a liquid crystal projector utilizing a liquid crystal device to project an image. It projects the light of an image that is displayed by the liquid crystal device on a screen  30  to display a projected image  40 . The image may be projected on a surface other than screen  30 ; it may be projected on a wall surface. 
     Projector  10  includes a remote controller signal reception unit  20  receiving an infrared modulated, remote controller signal transmitted from a remote controller  50  operated by a user, and an input unit  60 . The remote controller signal includes a command signal for remotely controlling projector  10 . Input unit  60  includes an input port for receiving an image signal supplied from an external signal supply device (not shown). The signal supply device includes a digital signal supply device outputting digital signals of a digital versatile disc (DVD) reproduction device, a Blu-ray disc reproduction device or the like, and an analog signal supply device outputting an analog signal of a computer or the like. 
       FIG. 2  shows a configuration of projector  10  shown in  FIG. 1 . 
     With reference to  FIG. 2 , projector  10  includes a receiver  62 , an image signal processing circuit  64 , a composite unit  66 , an image distortion correction unit  68 , a microcomputer  70 , an on-screen-display (OSD) circuit  72 , a digital analog converter (DAC)  74 , a liquid crystal display drive unit  76 , an optical system  78 , a power supply unit  80 , a connector  84 , and a lamp  86 . 
     Microcomputer  70  is operative in response to a command signal received from remote controller  50  via remote controller signal reception unit  20  to generate and output a control command to each component of projector  10 . 
     Receiver  62  receives an image signal from input unit  60  and outputs the image signal. Receiver  62  has an analog digital converter (ADC) function converting a received analog image signal to a digital signal, and an authentication function and a decryption function following a high-bandwidth digital content protection (HDCP) system. The HDCP is used to implement encrypting data transmitted in accordance with high definition multimedia interface (HDMI). This can prevent image signals or the like contents transmitted on digital transmission lines from being maliciously copied. While in this scenario the digital transmission line is a line transmitting data and signals in accordance with the HDMI, it may be a transmission line in accordance with digital visual interface (DVI). 
     Image signal processing circuit  64  receives an image signal from receiver  62 , processes the received signal into a signal for displaying, and outputs the processed signal. More specifically, image signal processing circuit  64  receives an image signal from receiver  62  and writes the signal to a frame memory (not shown) for each one frame (or screen), and also reads an image stored in the frame memory. In this writing and reading process, a variety of image processings are performed to convert a received image signal to generate an image signal, i.e., image data, for an image to be projected. 
     OSD circuit  72  follows an instruction received from microcomputer  70  to generate: characters and symbols representing a variety of statuses of projector  10 ; a menu image used in correcting image distortion, adjusting image quality, setting conditions for operations and the like; a pointer image, an underline image and other ornamental images; and the like (hereinafter collectively referred to as an “OSD image”) as an OSD image signal, and output the signal to composite unit  66 . 
     Composite unit  66  composites the OSD image signal and the image signal output from image signal processing circuit  64  to generate a composite image signal in the form of image data, and supplies the image data to image distortion correction unit  68 . 
     Note that the OSD image signal is generated by OSD circuit  72  reading OSD data stored in OSD circuit  72  at a memory (not shown) as the user issues an instruction via remote controller  50  to display an OSD image. If the OSD image is not displayed, composite unit  66  does not perform the above described composite process, and the image data output from image signal processing circuit  64  is exactly supplied to image distortion correction unit  68 . 
     Image distortion correction unit  68  corrects image distortion caused by relative inclination between the optical axis of light projected from projector  10  and a projection surface of screen  30 . More specifically, image distortion correction unit  68  receives the composite image signal from composite unit  66  and adjusts the signal to generate an image signal representing an image having distortion corrected, and outputs the generated image signal to DAC  74 . 
     More specifically, image distortion correction unit  68  corrects a projected image&#39;s distortion by forming a distorted image on each liquid crystal panel, as based on an amount of displacement corresponding to the user&#39;s operation and introduced at four corners of the projected image displayed on screen  30 . Hereinafter, in the embodiments, such correction will be referred to as “corner distortion correction”. Corner distortion correction will be described more specifically hereinafter. 
     DAC  74  receives an image signal from image distortion correction unit  68 , converts the received signal to an analog signal, and outputs the analog signal to liquid crystal display drive unit  76 . 
     Liquid crystal display drive unit  76 , optical system  78  and lamp  86  correspond to a projection unit controlled by microcomputer  70  to operate in response to the image signal output from DAC  74  to project an image on screen  30 . 
     The projection unit operates, as will be described hereinafter. Lamp  86  serving as an illumination device is for example a supervoltage mercury lamp, a metal halide lamp, a xenon lamp or the like. Lamp  86  is detachably attached via connector  84  to projector  10 . From lamp  86 , light is substantially collimated and thus emitted to liquid crystal display drive unit  76 . 
     Liquid crystal display drive unit  76  includes an optical system including a lens and a prism (not shown), and R, G, B liquid crystal panels. Liquid crystal display drive unit  76  receives light from lamp  86  and passes the light through its internal lens system (not shown), and the light is incident on each of the R, G, B liquid crystal panels such that a uniform distribution in quantity of light is achieved. Of the light incident via the lens system, light of a blue color wavelength band (hereinafter referred to as “B light”), light of a red color wavelength band (hereinafter referred to as “R light”), and light of a green color wavelength band (hereinafter referred to as “G light”) are substantially collimated and thus incident on the R, G, B liquid crystal panels. Each liquid crystal panel is driven in accordance with an image signal corresponding to R, G, B provided from DAC  74 , and modulates light in accordance with its driven status. The R light, G light, B light modulated by the liquid crystal panels are composited in color by a diachronic prism, and subsequently enlarged and thus projected by a projection lens on screen  30 . The projection lens includes a group of lenses imaging projected light on screen  30 , and an actuator for changing some of the lenses in the direction of the optical axis to adjust the projected image&#39;s zoomed and focused states. 
     Power supply unit  80  is supplied with power via a plug  82  plugged in a receptacle of an alternating current (AC) power supply (not shown), and supplies the received power to each component internal to projector  10 . 
     The user can use remote controller  50  to input a variety of inputs. Remote controller  50  transmits a remote controller signal, which is in turn input via remote controller signal reception unit  20  to microcomputer  70  to perform a variety of processes corresponding thereto. 
       FIG. 3  illustrates remote controller  50 . With reference to  FIG. 3 , remote controller  50  includes adjustment buttons  52 U,  52 D,  52 L,  52 R, an Enter button  54 , and a Keystone remote controller button  56 . The adjustment buttons are an upper adjustment button  52 U, a lower adjustment button  52 D, a left adjustment button  52 L, and a right adjustment button  52 R arranged in the form of a cross. In the following description, the four upper, lower, right and left buttons will also collectively be referred to as an adjustment button  52 . 
     When a corner distortion correction process is performed, adjustment button  52  outputs an upper left corner operation signal corresponding to right adjustment button  52 R and lower adjustment button  52 D, an upper right corner operation signal corresponding to left adjustment button  52 L and lower adjustment button  52 D, a lower left corner operation signal corresponding to right adjustment button  52 R and upper adjustment button  52 U, and a lower right corner operation signal corresponding to left adjustment button  52 L and upper adjustment button  52 U. The upper left corner operation signal is associated with an amount of displacement introduced at the upper left corner on the screen. The upper right corner operation signal is associated with an amount of displacement introduced at the upper right corner on the screen. The lower left corner operation signal is associated with an amount of displacement introduced at the lower left corner on the screen. The lower right corner operation signal is associated with an amount of displacement introduced at the lower right corner on the screen. 
     Thus, when the corner distortion correction process is performed, the user operates adjustment button  52  to set by how much amounts an image displayed on screen  30  has its four corners displaced. Image distortion correction unit  68  can correct image distortion in accordance with the amounts set for the four corners for displacement. Image distortion is corrected in a process having a procedure, as described hereinafter. 
     Image Distortion Correction Process 
     Initially, the user presses the remote controller  50  Keystone remote controller button  56 . In response, an image distortion correction process is selected and started. When the image distortion correction process is selected and started, OSD circuit  72  ( FIG. 2 ) operates to display an image distortion correction image on the same screen as projected image  40 . 
       FIG. 4  illustrates the image distortion correction image. With reference to  FIG. 4 , when the user presses the remote controller  50  Keystone remote controller button  56 , OSD circuit  72  operates to display the image distortion correction image. The image distortion correction image is formed of a corner distortion correction image G 1 , and a correction pattern PT 1 , PT 2 , PTC 1 -PTC 4  used to allow the user to designate a correction point. 
     Corner distortion correction image G 1  displays a type of an operation menu (an image distortion correction menu), and an indicator indicating how adjustment button  52  ( FIG. 3 ) is operated. 
     In the figure, correction points A, B, C, D represent four corners of an image displayed on screen  30 . In corner distortion correction, correction points A, B, C, D are positionally corrected in response to an operation signal output from adjustment button  52  (the upper left corner operation signal, the upper right corner operation signal, the lower left corner operation signal, and the lower right corner operation signal) to correct a distortion of an image displayed on screen  30 . 
     In the  FIG. 4  example, right adjustment button  52 R and lower adjustment button  52 D are associated with how correction point B (the upper left corner) is displaced. When the user presses right adjustment button  52 R and lower adjustment button  52 D to displace correction point B, corner distortion correction image G 1  displays an indicator indicating how right adjustment button  52 R and lower adjustment button  52 D are operated. 
     In that condition when the user presses right adjustment button  52 R and lower adjustment button  52 D, then, as shown in  FIG. 5 , in corner distortion correction image G 1 , the indicator corresponding to right adjustment button  52 R and lower adjustment button  52 D is turned on (or a color displayed is changed). Furthermore, on the same screen as projected image  40 , a marker M 1  is displayed to indicate that correction point B is subject to displacement. 
     In the  FIG. 5  example, how many times right adjustment button  52 R and lower adjustment button  52 D are pressed corresponds to by how much amount correction point B is displaced. Image distortion correction unit  68  adjusts an image signal, depending on by how much amount correction point B is displaced, to determine an image formation region in a pixel region of each liquid crystal panel for forming a (real) image based on the image signal. 
     More specifically, image distortion correction unit  68  displaces correction point B in a direction indicated by an arrow by an amount corresponding to how many times right adjustment button  52 R and lower adjustment button  52 D are pressed. Correction point B is displaced to a correction point B 1 . Thus a correction point on screen  30  that corresponds to correction point B 1  of the real image on each liquid crystal panel is displaced by an amount corresponding to how many times right adjustment button  52 R and lower adjustment button  52 D are pressed. Thus, the image data is corrected to: displace a correction point of an image formation region for forming a real image so that image distortion is corrected and the real image is projected on screen  30  in a normal form; and also minimize the optical transmittance of each pixel included in a region that does not contribute to forming the image. Consequently, the real image is displayed on screen  30  in the normal form. 
     On the other hand, although not shown, when the user presses left adjustment button  52 L and lower adjustment button  52 D, then, in corner distortion correction image G 1 , an indicator corresponding to left adjustment button  52 L and lower adjustment button  52 D is turned on, and correction point C is displaced by an amount corresponding to how many times left adjustment button  52 L and lower adjustment button  52 D are pressed. 
     Furthermore, when the user presses left adjustment button  52 L and upper adjustment button  52 U, then, in corner distortion correction image G 1 , an indicator corresponding to left adjustment button  52 L and upper adjustment button  52 U is turned on, and correction point D is displaced by an amount corresponding to how many times left adjustment button  52 L and upper adjustment button  52 U are pressed. 
     Furthermore, when the user presses right adjustment button  52 R and upper adjustment button  52 U, then, in corner distortion correction image G 1 , an indicator corresponding to right adjustment button  52 R and upper adjustment button  52 U is turned on, and correction point A is displaced by an amount corresponding to how many times right adjustment button  52 R and upper adjustment button  52 U are pressed. 
     Herein, as shown in  FIG. 4  and  FIG. 5 , when corner distortion correction is performed, correction pattern PT 1 , PT 2 , PTC 1 -PTC 4  used to allow the user to designate a correction point is projected on projected image  40 . 
     The correction pattern is formed for example by combining two or more of rectangular frame images PT 1 , PT 2 , PTC 1 -PTC 4  substantially similar in form to each liquid crystal panel&#39;s pixel region. The two or more of frame images PT 1 , PT 2 , PTC 1 -PTC 4  are superposed on projected image  40  and thus displayed. 
     More specifically, when the user presses Keystone remote controller button  56 , OSD circuit  72  is instructed by microcomputer  70  to read OSD data about a correction pattern stored in a memory and output the read OSD data to composite unit  66 . Composite unit  66  composites the OSD data about the correction pattern with an image signal output from image signal processing circuit  64  to generate a composite image signal in the form of image data. By such an operation, correction pattern PT 1 , PT 2 , PTC 1 -PTC 4  is projected on projected image  40  in performing the corner distortion correction process. 
     Thus the user can see how the correction pattern&#39;s frame images are distorted on screen  30  to visually, easily observe how projected image  40  is distorted. This allows image distortion correction to be done with precision and enhanced in operability. 
     If the correction pattern is displayed in a color identical or similar to that used to display projected image  40 , however, the correction pattern is visually less observable. As a result, the user has difficulty in visually observing how projected image  40  is distorted, resulting in poor operability in image distortion correction. 
     To overcome such disadvantage, OSD circuit  72  switches a color used to display the correction pattern and thus projects it on projected image  40 . OSD circuit  72  instructed by microcomputer  70  to control switching a color to be displayed allows the correction pattern to be displayed on the same screen as projected image  40  in a color different from that used to display projected image  40 . 
     Controlling How Color to be Displayed is Switched 
     In the first embodiment, the image distortion correction process is performed with the correction pattern displayed in a color switched as controlled in a process, as will be described hereinafter with reference to  FIG. 6 . 
       FIG. 6  is a flowchart for illustrating a process according to the first embodiment for controlling how a color that is displayed is switched. Note that the  FIG. 6  process has each step implemented by microcomputer  70  executing a previously stored program. 
     With reference to  FIG. 6 , initially, microcomputer  70  determines from a remote controller signal received by remote controller signal reception unit  20  ( FIG. 1 ) whether Keystone remote controller button  56  ( FIG. 3 ) has been operated (or pressed) (step S 01 ) If not (NO at S 01 ), the image distortion correction process is not selected. Accordingly, the image distortion correction image ( FIG. 4 ) is not displayed on screen  30 , and an image based on an image signal output from image signal processing circuit  64  is instead displayed on the screen (step S 03 ). 
     If microcomputer  70  determines that Keystone remote controller button  56  has been operated (YES at S 01 ), microcomputer  70  determines from a remote controller signal whether the user has designated a color for the correction pattern (step S 02 ). 
     The color is designated through an operation, as will be described hereinafter. When Keystone remote controller button  56  is pressed, the image distortion correction process is selected, and image distortion correction is now available. At the time, the image distortion correction image is displayed on screen  30 . 
     When the user desires to change a color used to display the correction pattern, or frame images PT 1 , PT 2 , PTC 1 -PTC 4 , the user presses a menu button of remote controller  50 . When the menu button is pressed, such an adjustment item screen as shown in  FIG. 7  is displayed on screen  30 . At a left side on the screen are displayed adjustment items aligned vertically. A mark indicating that an item has been selected is displayed on a right side of the item. When the menu button is operated to move the mark upward/downward to select “Screen”, as indicated in the figure, then, on a right side of the screen, adjustment items associated with image distortion correction are vertically aligned and thus displayed. Then, the menu button is operated to select an adjustment item (“Corner pattern” indicated in the figure) for the correction pattern. Furthermore, the menu button is operated to select a color used to display the correction pattern. 
     In the  FIG. 7  example, red is selected as a color used to display the correction pattern. The color is configured to be selectable from a plurality of colors such as red, blue, white and other colors. In  FIG. 7 , whenever the menu button is pressed once, the plurality of colors are switched and thus displayed. When a color to be displayed is selected and Enter button  54  ( FIG. 3 ) is pressed, the selected color is determined as a color to be displayed, and is used to display the correction pattern (or frame images PT 1 , PT 2 , PTC 1 -PTC 4 ). 
     Again, with reference to  FIG. 6 , when the user designates a color for the correction pattern (YES at step S 02 ), microcomputer  70  controls OSD circuit  72  to use the designated color to display the correction pattern (the  FIG. 4  frame images PT 1 , PT 2 , PTC 1 -PTC 4 ) (step S 04 ). On the other hand, when no color is designated for the correction pattern (NO at step S 02 ), microcomputer  70  controls OSD circuit  72  to use a predefined reference color, such as white, to display the correction pattern (step S 05 ). 
     Subsequently, microcomputer  70  determines from a remote controller signal whether adjustment button  52  ( FIG. 3 ) has been operated (or pressed) (step S 06 ). If so (YES at S 06 ), image distortion correction unit  68  is instructed by microcomputer  70  to employ the above described method and operate in response to an operation signal output from adjustment button  52  (i.e., the upper left corner operation signal, the upper right corner operation signal, the lower left corner operation signal, and the lower right corner operation signal) to positionally correct correction points A, B, C, D to correct a distortion of an image displayed on screen  30  (step S 07 ). 
     In step S 08 , microcomputer  70  determines from a remote controller signal whether image distortion correction should be ended. In step S 08  when Enter button  54  is pressed (YES at step S 08 ) the image distortion correction process ends. Accordingly, the correction pattern is no longer displayed on screen  30  (step S 10 ). 
     In contrast, when Enter button  54  is not pressed (NO at step S 08 ), the control returns to step S 06  and continues to wait for an input until adjustment button  52  is operated. Until Enter button  54  is pressed, steps S 06  and S 07  are repeated. Image distortion can thus be corrected. 
     In contrast, if in step S 06  microcomputer  70  determines that adjustment button  52  has not been operated (NO at step S 06 ), then, microcomputer  70  determines whether a predetermined period of time has elapsed since Keystone remote controller button  56  was pressed in step S 04 , i.e., whether adjustment button  52  is unoperated for the predetermined period of time (step S 09 ). If so (YES at step S 09 ), the control proceeds to step S 10  to end the image distortion correction process, and the correction pattern is no longer displayed. If adjustment button  52  is not unoperated for the predetermined period of time (NO at step S 09 ), the control returns to step S 06  and until adjustment button  52  is operated the control continues to wait for an input. 
     As described above, the present invention in the first embodiment allows how a color used to display a correction pattern is switched to be controlled to allow the correction pattern to be displayed on the same screen as a projected image in a color different from that used to display the projected image. Furthermore, the present invention in the first embodiment allows switching a color that is displayed to be controlled in accordance with a color to be displayed, as selected by the user. This can enhance the correction pattern&#39;s visual observability and hence help the user to visually observe how the projected image is distorted. As a result, image distortion correction is enhanced in operability. 
     Second Embodiment 
     The present invention in a second embodiment provides an image distortion correction process performed with a correction pattern displayed in a color switched, as controlled in a process, as will be described hereinafter with reference to  FIG. 8 . 
     With reference to  FIG. 8 , in the second embodiment, a color to be displayed is toggled between a preset plurality of colors whenever a predetermined period of time elapses. In the  FIG. 8  example, a color used to display the correction pattern is switched to white followed by red and then by blue whenever a predetermined period of time T elapses. 
       FIG. 9  is a flowchart for illustrating a process according to the second embodiment for controlling how a color that is displayed is switched. Note that the  FIG. 9  process has each step implemented by microcomputer  70  executing a previously stored program. 
     With reference to  FIG. 9 , the second embodiment provides a process different from the  FIG. 6  flowchart only in that steps S 02 -S 05  are replaced with steps S 22 -S 24 . 
     In  FIG. 9 , initially, microcomputer  70  determines from a remote controller signal received by remote controller signal reception unit  20  whether Keystone remote controller button  56  has been operated (or pressed) (step S 01 ). If not (NO at S 01 ), the image distortion correction process is not selected. Accordingly, the image distortion correction image ( FIG. 4 ) is not displayed on screen  30 , and an image based on an image signal output from image signal processing circuit  64  is instead displayed on the screen (step S 23 ), 
     If microcomputer  70  determines that Keystone remote controller button  56  has been operated (YES at S 01 ), microcomputer  70  starts a timer to count time (step S 22 ), and microcomputer  70  controls OSD circuit  72  to toggle a color that is used to display the correction pattern between a plurality of colors whenever the preset, predetermined period of time T elapses, as based on a value counted by the timer (step S 24 ). Thus, the correction pattern, or frame images PT 1 , PT 2 , PTC 1 -PTC 4 , is displayed in a color toggling as shown in  FIG. 8 . 
     As described above, the present invention in the second embodiment allows a correction pattern to be displayed in a color toggling between a preset plurality of colors whenever a predetermined period of time elapses. Even if the image distortion correction process is performed with a projected image displayed in a diversely changing color, the correction pattern&#39;s visual observability can be ensured, and the user can visually, easily observe how the projected image is distorted. As a result, image distortion correction is enhanced in operability. 
     Exemplary Variation 
     While the  FIG. 9  process has been described for an image distortion correction process performed with a correction pattern toggled in color and thus displayed, it is also possible that when the correction pattern is toggled in color and thus displayed and the user also starts to operate adjustment button  52 , the toggling can be stopped so that thereafter the correction pattern may be displayed constantly in a color that was applied when the user started to operate adjustment button  52 . 
       FIG. 10  is a flowchart for illustrating a process according to the second embodiment in an exemplary variation for controlling how a color that is displayed is switched. With reference to  FIG. 10 , the second embodiment in the exemplary variation provides a process different from the  FIG. 9  flowchart only in that step S 061  is additionally introduced between steps S 06  and S 07 . 
     In  FIG. 10  when the control determines in step S 06  that adjustment button  52  has been operated (YES at S 06 ), OSD circuit  72  is instructed by microcomputer  70  to stop toggling a color that is displayed (step S 061 ). This allows the correction pattern to be thereafter displayed constantly in a color that was applied when the user operated adjustment button  52 . 
     Thus the present exemplary variation allows a color that is displayed to be switched as controlled in a process so that a correction pattern is displayed in a toggled color, and the user operating adjustment button  52  is regarded as the user designating a color to be displayed and the color to be displayed is thus fixed. In other words, the correction pattern is displayed substantially in a color selected by the user. This allows the correction pattern to be automatically displayed in an optimum color without requiring the user to perform an operation to designate a color, and can thus improve operability in image distortion correction. 
     If in  FIG. 10  at step S 061 , toggling and thus displaying is stopped, and in that condition, the user has finished operating adjustment button  52 , then, thereafter, when a predetermined period of time elapses, toggling and thus displaying may be resumed. 
     Third Embodiment 
     A third embodiment provides an image distortion correction process performed with a correction pattern displayed in a color switched, as controlled in a process, as will be described hereinafter with reference to  FIG. 11 . 
       FIG. 11  is a flowchart for illustrating a process according to the third embodiment for controlling how a color that is displayed is switched. Note that the  FIG. 11  process has each step implemented by microcomputer  70  executing a previously stored program. 
     With reference to  FIG. 11 , the third embodiment provides a process different from the  FIG. 6  flowchart only in that steps S 02 -S 05  are replaced with steps S 31 -S 34 . 
     In  FIG. 11 , initially, microcomputer  70  determines from a remote controller signal received by remote controller signal reception unit  20  whether Keystone remote controller button  56  has been operated (or pressed) (step S 01 ). If not (NO at S 01 ), the image distortion correction process is not selected. Accordingly, the image distortion correction image ( FIG. 4 ) is not displayed on screen  30 , and an image based on an image signal output from image signal processing circuit  64  is instead displayed on the screen (step S 32 ). 
     If microcomputer  70  determines that Keystone remote controller button  56  has been operated (YES at S 01 ), microcomputer  70  reads color information of an image signal from image signal processing circuit  64  (step S 31 ), and determines from the read color information a color used to display the correction pattern (step S 33 ). 
     More specifically, microcomputer  70  selects a hue for the correction pattern in accordance with at least one of the hue, saturation and lightness of an image signal, as based on the read color information, and outputs the selected hue to OSD circuit  72 . OSD circuit  72  is instructed by microcomputer  70  to read OSD data from memory about a correction pattern that has the selected hue as a color used to display it, and output the OSD data to composite unit  66 . Composite unit  66  composites the OSD data about the correction pattern with an image signal output from image signal processing circuit  64  to generate a composite image signal in the form of image data. By such an operation, the correction pattern is displayed in a color determined in step S 33  (step S 34 ). 
     In selecting a hue, for example, a color complementary to the hue of an image signal is selected as a hue for the correction pattern. The correction pattern displayed in the complementary color (a hue positionally opposite in the color wheel) can be perceived as a color of a combination most intensified in contrast. The correction pattern can thus be visually more observable, and the user can visually, easily observe how a projected image is distorted. This allows image distortion correction to be enhanced in operability. 
     Note that a hue may not be selected for the correction pattern, as based only on the hue of the entirety of an image signal; it may be selected for the correction pattern, as based on that information of the image signal of the hue, saturation or lightness of a portion in a vicinity of frame images PT 1 , PT 2 , PTC 1 -PTC 4  ( FIG. 4 ) of the correction pattern. 
     As has been described above, the present invention in the third embodiment allows an image signal&#39;s color information to be considered in switching a color used to display a correction pattern. Even if the image distortion correction process is performed with a projected image displayed in a diversely changing color, the correction pattern&#39;s visual observability can be ensured. In particular, a color complementary to the hue of the image signal can be selected as a color used to display the correction pattern. This allows the correction pattern to be easily observed, and the user to visually, easily observe how the projected image is distorted. As a result, image distortion correction is enhanced in operability. 
     While the embodiments have been described for a projector provided in the form of a liquid crystal projector, the present invention is not limited thereto. For example, the present invention is applicable to a projector in a digital light processing (DLP)® system or a similar, different system. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted by the terms of the appended claims.