Patent Publication Number: US-9841662-B2

Title: Projector and method for controlling projector

Description:
The present application is a continuation application of U.S. patent application Ser. No. 14/623,120 filed on Feb. 16, 2015, which claims priority from U.S. patent application Ser. No. 13/628,731 filed on Sep. 27, 2012, which claims priority from Japanese Patent Application No. 2011-216716 filed Sep. 30, 2011 and Japanese Patent Application No. 2011-216327 filed Sep. 30, 2011, which are hereby expressly incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a projector and a method for controlling the projector. 
     2. Related Art 
     There has been a known method for projecting an image from a projector and geometrically correcting the projected image on a user interface screen of a computer. For example, there has been a known geometric correction interface using an auxiliary line (Japanese Patent No. 3,845,386), in which application software that runs on a computer virtually narrows the area of a user interface screen and displays the thus narrowed screen to provide a virtual correction area that allows a user to correct an auxiliary line that does not fall within the screen and perform auxiliary-line-based correction even when a display having resolution lower than the panel size of the projector is used. 
     Further, there has been a known projector that allows a user to display an image for the correction to readily correct trapezoidal distortion produced depending on the angle at which a projector is installed with respect to a projection surface (see JP-A-2010-250041, for example). 
     In the correction method described in Japanese Patent No. 3,845,386, however, it is necessary to use a computer having application software for correction installed therein to geometrically correct the projection screen of a projector. The correction cannot therefore be made by using the projector alone. Further, the user has to make correction while comparing the display screen of the computer with the projection screen projected from the projector. It has therefore been desired to provide a projector that allows the user to geometrically correct a projected image (correct the shape of a projected image) by using the projector alone based on simple operation. 
     Further, an image projected by a projector is sometimes distorted, what is called pincushion distortion, depending on the state of the projection surface. Since pincushion distortion cannot be corrected only by moving the corners of the projected image, the configuration of the related art described above cannot solve the problem. It has therefore been desired to provide a projector that allows the user to readily correct pincushion distortion. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide a projector that allows a user to geometrically correct a projected image (correct the shape of a projected image) by using the projector alone based on simple operation and a method for controlling the projector. 
     Another advantage of some aspects of the invention is to provide a projector that allows the user to readily correct pincushion distortion (i.e., arc correction) and a method for controlling the projector. 
     The present invention can be implemented in the following forms or application examples. 
     An aspect of the invention is directed to a projector that projects an image and includes an operation reception unit that receives input operation, a selection unit that allows selection of one of a plurality of controlled objects located in correspondence with vertices of a contour of the image and sides of the contour, and a correction unit that allows movement of the controlled object selected by using the selection unit within the image based on the input operation and corrects the contour of the image based on the moved controlled object. 
     According to the projector described above, one of the controlled objects located in correspondence with the vertices of the contour of an image projected by the projector and the sides of the contour is selected, and the selected controlled object is moved based on input operation. The contour is then corrected based on the moved controlled object. The user can therefore correct the geometric shape of the contour of the image by moving any of the controlled objects of the image, which is a function of the projector. 
     The projector described above may be configured such that the selection unit is a control point selection unit that handles the vertices of the contour of the image based on the image information and predetermined points located on the sides of the contour as control points that are the controlled objects and allows selection of one of the plurality of control points as a selected control point, and the correction unit includes a control point movement unit that allows movement of the selected control point selected by using the control point selection unit within the image based on the input operation and an image correction unit that forms a contour of the image in such a way that the contour passes through the selected control point moved by using the control point movement unit and corrects the image information to fit in the formed contour. 
     According to the projector described above, the selection unit handles the vertices of the contour of the image and predetermined points located on the sides of the contour as control points and allows selection of one of the control points as a selected control point. The control point movement unit provided in the correction unit allows movement of the selected control point within the image based on the input operation, and the image correction unit forms a contour of the image in such a way that the contour passes through the selected control point moved by using the control point movement unit and corrects the image information to fit in the formed contour. The user can therefore correct the shape of the contour of the image by moving the selected control point. The projector then corrects the image information to fit in the contour having the corrected shape. The geometric shape of the image based on the image information can thus be corrected by using the projector alone. 
     The projector described above may be configured such that the image correction unit forms a contour of the image in such a way that the selected control point is connected to an adjacent one of the control points with a curve. 
     According to the projector described above, the image correction unit forms an image by connecting the control point to an adjacent one of the control points with a curve. As a result, the image has a contour including the curve, and the image information corrected by the image correction unit represents an image having a curved contour. Projecting the thus formed image having a curved contour can cancel curved distortion of the image on a curved projection surface. 
     The projector described above may be configured such that each of the predetermined points is at least one point located on the corresponding side of the contour. 
     According to the projector described above, each of the predetermined points is at least one point located on the corresponding side of the contour. The thus set predetermined points along with the four vertices form at least eight control points in total, which allow formation of a contour of the image, whereby the projector can be operated in a simple, effective manner. 
     The projector described above may be configured such that a default position of each of the predetermined points is the center of the corresponding side of the contour. 
     According to the projector described above, a default position of each of the predetermined points is the center of the corresponding side of the contour. The user can therefore form an image formation region in a well balanced manner. 
     The projector described above may be configured such that each of the predetermined points is movable based on the input operation along a line connecting the default position to the center of the image. 
     According to the projector described above, each of the predetermined points is movable along a line connecting the default position to the center of a pixel region. The formation of an image formation region, correction of image information, and other software processing can therefore be simplified. 
     The projector described above may be configured to further include alight source, a light modulator that modulates light emitted from the light source, a projection system that projects image light modulated by the light modulator, and an identification image display unit that projects the image light through the projection system to display eight identification images corresponding to four corners of the image carried by the image light and four sides between the corners. The selection unit may include a selection operation unit that receives operation of selecting one of the eight identification images displayed by the identification image display unit, an enhancement display unit that enhances the identification image selected by the selection operation unit to be distinguishable from the other identification images and displays the enhanced identification image, and a movement operation unit that, in a state in which the enhancement display unit displays the enhanced identification image, receives operation of moving the controlled object located at the corner or in a predetermined position on the side. The correction unit moves the corner or the predetermined position on the side corresponding to the identification image selected by the selection operation unit based on the operation received by the movement operation unit and corrects pincushion distortion based on the movement. 
     The projector described above displays the eight identification images corresponding to the four corners and the four sides of a projected image, selects one of the identification images and displays the selected identification image, and corrects pincushion distortion based on operation on the identification image, whereby operation of correcting the pincushion distortion can be readily carried out. 
     The projector described above may be configured such that the enhancement display unit adds direction marks that correspond to at least two axes and are movable by using the movement operation unit to the identification image selected by using the selection operation unit from the identification images corresponding to the corners and adds a direction mark that corresponds to one axis and is movable by using the movement operation unit to the identification image selected by using the selection operation unit from the identification images corresponding to the sides. 
     According to the projector described above, since optimum direction marks are added to the corners and sides and displayed, the user can be guided to appropriate operation, whereby the operation of correcting pincushion distortion can be more readily carried out. 
     The projector described above may be configured to be capable of choosing an operation mode thereof between a pincushion distortion correction mode in which pincushion distortion is corrected and a trapezoidal distortion correction mode in which trapezoidal distortion is corrected. In the trapezoidal distortion correction mode, the identification image display unit may display four identification images corresponding to the four corners of the image. The selection operation unit may receive operation of selecting one of the four identification images displayed by the identification image display unit. In a state in which the enhancement display unit displays the selected identification image, the movement operation unit may receive operation of moving the corner. The image correction unit may move the corner corresponding to the identification image selected by using the selection operation unit based on the operation received by the movement operation unit and correct trapezoidal distortion based on the movement. 
     According to the projector described above, operation of correcting trapezoidal distortion can be readily carried out as well as operation of correcting pincushion distortion. 
     The projector described above may be configured such that the enhancement display unit disables display of the other seven identification images that have not been selected by using the selection operation unit in the pincushion distortion correction mode whereas disabling display of the other three identification images that have not been selected by using the selection operation unit in the trapezoidal distortion correction mode. 
     According to the projector described above, the operation of correcting pincushion distortion and trapezoidal distortion can be more readily carried out under optimum display. 
     The projector described above may be configured such that, in a state in which the corner or the predetermined position on the side selected by using the selection operation unit is located at a limit of a movable range and hence unable to move in a predetermined direction, the enhancement display unit reduces visibility of the direction mark corresponding to the predetermined direction. 
     According to the projector described above, the state of the displayed direction mark notifies the user of the limit of the operation of moving the corner or the side, whereby the operation of correcting pincushion distortion can be more readily carried out. 
     Another aspect of the invention is directed to a method for controlling a projector that projects an image based on image information and includes selecting one of a plurality of controlled objects located in correspondence with vertices of a contour of the image based on the image information and sides of the contour, moving the controlled object selected in the selecting within the image based on input operation; and correcting the contour of the image based on the controlled object moved in the moving. 
     According to the method for controlling a projector described above, one of the controlled objects located in correspondence with the vertices of the contour of an image projected by the projector and the sides of the contour is selected, and the selected controlled object is moved based on input operation. The contour is then corrected based on the moved controlled object. The user can therefore correct the geometric shape of the contour of the image by moving any of the controlled objects of the image, which is a function of the projector. 
     The method for controlling a projector described above may be configured such that the selecting is a control point selection in which the vertices of the contour of the image based on the image information and predetermined points located on the sides of the contour are handled as control points that are the controlled objects and one of the plurality of control points is selected as a selected control point. In the moving, the selected control point selected in the control point selection may be moved within the image based on the input operation. In the correcting, a contour of the image may be so formed that the contour passes through the selected control point moved in the moving and the image information is corrected to fit in the formed contour. 
     According to the method for controlling a projector described above, the user can correct the shape of the contour of the image by moving the selected control point. The projector then corrects the image information to fit in the contour having the corrected shape. The geometric shape of the image based on the image information can thus be corrected by using the projector alone. 
     The method for controlling a projector described above may be configured such that, in the selecting, image light is projected through a projection system to display eight identification images corresponding to four corners of the image carried by the image light and four sides between the corners. Operation of selecting one of the eight identification images may be received. The selected identification image may be so enhanced and displayed that the enhanced identification image is distinguishable from the other identification images. In the moving, in a state in which the enhanced identification image is displayed, operation of moving the corner or a predetermined position on the side may be received, and the corner or the predetermined position on the side corresponding to the identification image selected in the selecting may be moved based on the received operation. In the correcting, pincushion distortion may be corrected based on the movement in the moving. 
     The method for controlling a projector described above includes displaying the eight identification images corresponding to the four corners and the four sides of a projected image, selecting one of the identification images and displaying the selected identification image, and correcting pincushion distortion based on operation on the identification image, whereby operation of correcting the pincushion distortion can be readily carried out. 
     When the method for controlling the projector described above are configured by using a computer incorporated in the projector, the forms and the application examples described above can also be configured in the form of program for providing the functions of the projector and the method for controlling the projector or in the form of a recording medium or any other component on which the program is so recorded that the program is readable by the computer. Examples of the recording medium may include a variety of media readable by the computer, such as a flexible disk, an HDD (hard disk drive), a CD-ROM (compact disk read only memory), a DVD (digital versatile disk), a Blu-ray Disc®, an magneto-optical disk, a nonvolatile memory card, a storage device (RAM (random access memory), a ROM (read only memory), and any other semiconductor memory) built in the projector, and a storage device (such as USB memory) external to the projector. 
     According to the above aspects of the invention, the geometric shape of an image based on image information can be corrected by using a projector alone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a block diagram showing a schematic configuration of a projector according to a first embodiment. 
         FIG. 2  describes a menu image displayed by the projector. 
         FIG. 3  shows a projected image in which a control point area selection image for bow-shape correction is displayed. 
         FIGS. 4A and 4B  show projected images in each of which a bow-shape correction adjustment image is displayed.  FIG. 4A  shows a projected image including a corner adjustment image, and  FIG. 4B  shows a projected image including a side adjustment image. 
         FIG. 5  is a flowchart of the processes that the projector carries out to perform bow-shape correction. 
         FIG. 6  is a plan view showing a pixel region having undergone the bow-shape correction. 
         FIG. 7  is a block diagram showing a schematic configuration of a projector according to a second embodiment. 
         FIGS. 8A and 8B  describe trapezoidal distortion. FIG.  8 A is a side view of a projector and a projection surface viewed sideways, and  FIG. 8B  is a front view showing the projection surface. 
         FIGS. 9A to 9D  describe trapezoidal distortion.  FIG. 9A  is a side view of the projector and the projection surface viewed sideways.  FIGS. 9B and 9D  are front views showing the projection surface.  FIG. 9C  shows a pixel region of a liquid crystal light valve. 
         FIGS. 10A to 10H  describe pincushion distortion.  FIG. 10A  is a perspective view of the projector and the projection surface viewed obliquely downward.  FIGS. 10B, 10D, 10F, and 10H  show the pixel region of the liquid crystal light valve.  FIGS. 10C, 10E, and 10G  are front views showing the projection surface. 
         FIG. 11  is a flowchart for describing the operation of the projector when a trapezoidal distortion correction key or a pincushion distortion correction key is operated. 
         FIG. 12  is a flowchart for describing the operation of the projector when the pincushion distortion correction key is operated. 
         FIGS. 13A and 13B  show images displayed when trapezoidal distortion correction is in progress.  FIG. 13A  shows a corner selection image, and  FIG. 13B  shows a corner adjustment image. 
         FIGS. 14A to 141  describe a procedure of correcting trapezoidal distortion and are front views of the projection surface. 
         FIG. 15  shows an adjustment section selection image. 
         FIG. 16  shows a corner adjustment image. 
         FIG. 17  shows a side adjustment image. 
         FIGS. 18A to 18I  describe movement of a corner of an image formation region and show the pixel region of the liquid crystal light valve. 
         FIGS. 19A to 19C  describe movement of the middle point of a horizontal side of an image formation region and show the pixel region of the liquid crystal light valve. 
         FIGS. 20A to 20C  describe movement of the middle point of a vertical side of an image formation region and show the pixel region of the liquid crystal light valve. 
         FIGS. 21A to 21G  describe a procedure of correcting pincushion distortion and are front views showing the projection surface. 
         FIGS. 22A and 22B  describe the procedure of correcting pincushion distortion and show the pixel region of the liquid crystal light valve. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Projectors according to embodiments will be described below with reference to the drawings. 
     The embodiments presented below will be described with reference to a projector capable of correcting the shape of a projected image. The projector described in each of the embodiments is an optical apparatus that modulates light emitted from a light source to form an image based on externally inputted image information (hereinafter referred to as “input image”) and projects the image on a screen, a wall, or any other surface (hereinafter referred to as “projection surface”). 
     First Embodiment 
       FIG. 1  is a block diagram showing a schematic configuration of a projector according to a first embodiment. The internal configuration of the projector will be described with reference to  FIG. 1 . 
     A projector  1  includes an image projection unit  10 , a control unit  20 , a light source control unit  21 , an operation reception unit  22 , an operation signal reception unit  23 , a remote control  24 , an image information input unit  30 , an image processing unit  31 , an OSD processing unit  32 , and an image correction unit  33 , as shown in  FIG. 1 . 
     The image projection unit  10  includes a light source apparatus  11  as a light source, three liquid crystal light valves  12 R,  12 G, and  12 B as light modulators, a projection lens  13  as a projection system, and a liquid crystal driver  14 . In the image projection unit  10 , the liquid crystal light valves  12 R,  12 G, and  12 B modulate light outputted from the light source apparatus  11  into image light, and the projection lens  13  projects and displays the image light on a projection surface S. 
     The light source apparatus  11  includes a discharge-type light source lamp  11   a  formed, for example, of an ultra-high-pressure mercury lamp or a metal halide lamp, and a reflector  11   b  that reflects the light emitted from the light source lamp  11   a  toward the liquid crystal light valves  12 R,  12 G, and  12 B. The light outputted from the light source apparatus  11  is converted by an optical integration system (not shown) into light having a substantially uniform luminance distribution, separated by a color separation system (not shown) into red (R), green (G), and blue (B) color light components, which are three primary colors of light, and then incident on the liquid crystal light valves  12 R,  12 G, and  12 B. 
     Each of the liquid crystal light valves  12 R,  12 G, and  12 B is formed, for example, of a liquid crystal panel having a liquid crystal material sealed between a pair of transparent substrates. Each of the liquid crystal light valves  12 R,  12 G, and  12 B has a rectangular pixel region in which a plurality of pixels (not shown) are arranged in a matrix and can apply a drive voltage to the liquid crystal material on a pixel basis. When the liquid crystal driver  14  applies a drive voltage according to inputted image information to each of the pixels, the pixel sets its optical transmittance at a value according to the image information. As a result, the light outputted from the light source apparatus  11  is modulated when passing through the image regions of the liquid crystal light valves  12 R,  12 G, and  12 B to form image light fluxes corresponding to the three colors according to the image information. The thus formed image light fluxes corresponding to the three colors are combined on a pixel basis by a light combining system (not shown) into color image light, which is enlarged and projected by the projection lens  13 . 
     The control unit  20  includes a CPU (central processing unit), a RAM (random access memory) used to temporarily store a variety of data and other information, and a nonvolatile ROM (read only memory) and oversees the control of the operation of the projector  1  by instructing the CPU to operate in accordance with a control program stored in the ROM. That is, the control unit  20  functions as a computer. 
     The light source control unit  21  controls the light source apparatus  11  (light source lamp  11   a ) to go on based on an instruction from the control unit  20 . Specifically, the light source control unit  21  allows the light source lamp  11   a  to go on by supplying a predetermined amount of electricity to the light source lamp  11   a  and go off by stopping supplying the electricity. Further, the light source control unit  21  can adjust the luminance (brightness) of the light source lamp  11   a  by controlling the amount of electricity supplied to the light source lamp  11   a  based on an instruction from the control unit  20 . 
     The operation reception unit  22 , which receives user&#39;s input operation, includes a plurality of operation keys that allow the user to issue a variety of instructions to the projector  1 . The operation keys provided on the operation reception unit  22  include a power key for turning on and off a power supply, an input switch key for switching an inputted image signal from one to another, a menu key for displaying and hiding a menu image for setting a variety of items, four directional keys corresponding to the upward, downward, rightward, and leftward directions (upward key, downward key, rightward key, and leftward key), an enter key for accepting a variety of settings, and an ECS (escape) key used to cancel or otherwise deselect operation. When the user operates (presses) any of the variety of operation keys on the operation reception unit  22 , the operation reception unit  22  receives the input operation and outputs an operation signal according to the user&#39;s operation to the control unit  20 . 
     The remote control  24  includes a plurality of operation keys as the operation reception unit  22  does. When the user operates any of the variety of operation keys on the remote control  24 , the remote control  24  issues an operation signal in the form of infrared light or any other form according to the user&#39;s operation, and the operation signal reception unit  23  receives the operation signal and forward it to the control unit  20 . The operation signal reception unit  23 , which receives an operation signal from the operation reception unit  22  or the remote control  24 , corresponds to an operation reception unit in the appended claims. 
     The image information input unit  30  includes a plurality of input terminals, to which image information in a variety of formats is inputted from a video reproduction apparatus, a personal computer, and other external image supply apparatus (not shown). The image information input unit  30  outputs the inputted image information to the image processing unit  31 . 
     The image processing unit  31  converts the image information inputted from the image information input unit  30  into image information representing grayscales of the pixels of the liquid crystal light valves  12 R,  12 G, and  12 B, that is, image information for defining a drive voltage applied to each of the pixels. Further, the image processing unit  31  performs, for example, image quality adjustment for adjusting image quality, such as brightness, contrast, sharpness, and tint, on the converted image information based on an instruction from the control unit  20  and outputs the processed image information to the OSD processing unit  32 . 
     The OSD processing unit  32  overlays an OSD (on-screen display) image, such as the menu image and a message image, on an image according to inputted image information (hereinafter also referred to as “input image”) based on an instruction from the control unit  20 . The OSD processing unit  32  includes an OSD memory (not shown), which stores OSD image information representing figures, fonts, and other parameters for forming OSD images. When the control unit  20  instructs to overlay an OSD image, the OSD processing unit  32  reads necessary OSD image information from the OSD memory and combines the OSD image information with image information inputted from the image processing unit  31  in such a way that the OSD image is overlaid on the input image in a predetermined position. The image information with which the OSD image information combined is outputted to the image correction unit  33 . When the control unit  20  does not instruct to overlay an OSD image, the OSD processing unit  32  does not process image information inputted from the image processing unit  31  but directly outputs it to the image correction unit  33 . 
     The image correction unit  33  corrects curved distortion produced, for example, when an image is projected on a curved projection surface S (also referred to as “bow-shape correction”). Specifically, the image correction unit  33  sets an image formation region having a shape that cancels the curved distortion in the pixel region of each of the liquid crystal light valves  12 R,  12 G, and  12 B and not only corrects image information inputted from the OSD processing unit  32  in such a way that the input image is formed in the image formation region but also sets each pixel outside the image formation region at a black pixel value, that is, a pixel value that minimizes optical transmittance. 
     The image correction unit  33  outputs the thus corrected image information to the liquid crystal driver  14 . The projection surface S in the present embodiment is a concave surface, and hence an image projected on the projection surface S is displayed as a barrel-shaped curved image. The curved distortion can therefore be canceled by forming a pincushion-shaped image formation region in each of the pixel regions. When the control unit  20  does not instruct to correct curved distortion, the image correction unit  33  does not process image information inputted from the OSD processing unit  32  but directly outputs it to the liquid crystal driver  14 . In this case, the entirety of each of the pixel regions serves as the image formation region, and an image (input image) is formed over the entire pixel region. 
     When the liquid crystal driver  14  drives the liquid crystal light valves  12 R,  12 G, and  12 B in accordance with image information inputted from the image correction unit  33 , the liquid crystal light valves  12 R,  12 G, and  12 B produce modulated image light fluxes according to the image information, and the projection lens  13  projects the image light fluxes. 
     A description will next be made of the bow-shape correction (curved distortion correction) performed by the projector  1 . 
     The projector  1  according to the first embodiment can correct curved distortion by using the image correction unit  33  as described above. Specifically, when the menu key provided on the operation reception unit  22  or the remote control  24  is pressed, the menu image is displayed. When a bow-shape correction (curved distortion correction) item in the menu image is selected, a control point area selection image for allowing the user to select an area where curved distortion is corrected is displayed. When a desired control point area is selected in the control point area selection image, a curved distortion correction image corresponding to the selected control point area is displayed. In the curved distortion correction image, the user can move the control point by operating the direction keys to correct the curved distortion. In the present embodiment, the vertices at the four corners of the contour of an input image and four points located at the centers of the four sides of the contour are used as the control points. 
       FIG. 2  describes the menu image displayed by the projector  1  according to the present embodiment. 
     In the menu image M 1 , a plurality of items (adjustment items) are arranged in the vertical direction, as shown in  FIG. 2 . In the example shown in  FIG. 2 , the following four items are displayed: “bow-shape correction” for correcting curved distortion; “color mode” for setting an image quality adjustment mode (color mode); “brightness” for adjusting the brightness of an image; and “lamp luminance” for adjusting the luminance of the light source lamp  11   a . One of the four adjustment items (“bow-shape correction” in  FIG. 2 ) differs from the other items in terms of background color, which indicates that the item has been selected. The menu image M 1  is displayed by the OSD processing unit  32 . 
     In the state in which the menu image M 1  is displayed, the user can select a desired adjustment item by operating the upward and downward direction keys. When the user selects a desired adjustment item and operates the enter key, the selected adjustment item is accepted and a setting image associated with the adjustment item can be displayed. Further, the user can stop displaying the menu image M 1  by operating the ESC key. 
       FIG. 3  shows a projected image in which a control point area selection image for bow-shape correction is displayed. 
     A projected image A 1  is displayed with a control point area selection image N 1  overlaid thereon as an OSD image, as shown in  FIG. 3 . A character string “[bow-shape correction]” is displayed in an upper portion of the control point area selection image N 1 , and eight control point area images CA associated with the input image are displayed below the character string. The eight control point area images CA are formed of four control point area images CA (CA 1 , CA 3 , CA 6 , and CA 8 ) corresponding to control points CP (CP 1 , CP 3 , CP 6 , and CP 8 ) at the four corners of the input image and four control point area images CA (CA 2 , CA 4 , CA 5 , and CA 7 ) corresponding to control points CP (CP 2 , CP 4 , CP 5 , and CP 7 ) at the centers of the four sides of the input image. 
     One of the control point area images CA 1  to CA 8  (control point area image CA 1  in the example shown in  FIG. 3 ) is colored differently from the other seven, which indicates that the differently colored control point area image CA has been selected. In  FIG. 3 , the eight control points CP are displayed as visible “points,” but they are not visible in an actual projected image. 
     A character string “Select area” for prompting the user to select a control point area image CA is displayed in a lower portion of the control point area selection image N 1 . The following other character strings representing what the user can do are further displayed: change a control point area image (CA 1  to CA 8 ) to be selected by operating the upward, downward, rightward, and leftward direction keys; accept a control point area image CA by operating the enter key; and stop displaying the control point area selection image N 1  by operating the ESC key. The user can select a desired control point area image CA by operating the direction keys, and the selection of a control point area image CA is accepted by operating the enter key after the control point area image CA is selected. When the selection of a control point area image CA is accepted, a bow-shape correction adjustment image corresponding to the selected control point area image CA is displayed. The control point CP corresponding to the selected control point area image CA corresponds to a selected control point. In the bow-shape correction adjustment image, the position of the control point CP corresponding to the selected control point area image CA can be adjusted. 
       FIGS. 4A and 4B  show projected images in each of which a bow-shape correction adjustment image is displayed.  FIG. 4A  shows a projected image including a corner adjustment image, and  FIG. 4B  shows a projected image including a side adjustment image. 
     A projected image A 2  is displayed with a bow-shape correction adjustment image D (D 1 ) overlaid thereon as an OSD image, as shown in  FIG. 4A . A character string “[bow-shape correction]” is displayed in an upper portion of the bow-shape correction adjustment image D 1 . The control point area image CA 1  is enlarged and displayed as an enlarged image Z 1  below the character string. 
     The enlarged image Z 1  has additional triangular direction marks T pointing upward, downward, rightward, and leftward, which indicate that the corner displayed in the control point area image CA 1  (that is, control point CP 1 ) is movable upward, downward, rightward, and leftward (position is adjustable). Further, a message “Make adjustment” is displayed in a lower portion of the bow-shape correction adjustment image D 1 , prompting the user to adjust the position of the control point CP 1 . In the state in which the bow-shape correction adjustment image D 1  is displayed, the user can adjust the position of the control point CP 1  (corner) by operating the direction keys. When the position of the control point CP 1  is changed, the projected image A 2  is corrected to a bow-shape image based on the position of the control point CP 1  (curved distortion correction). 
     The following other character strings representing what the user can do are displayed in a lower portion of the bow-shape correction adjustment image D 1 : adjust the bow-shape correction by operation the upward, downward, rightward, and leftward direction keys; and terminate the adjustment and return to the control point area selection image N 1  by operating the enter key or the ESC key. It is noted that the range within which the position of the control point CP 1  is adjusted by operating the direction keys is limited to the pixel region of each of the liquid crystal light valves  12 R,  12 G, and  12 B. 
     A projected image A 3  is displayed with a bow-shape correction adjustment image D (D 2 ) overlaid thereon as an OSD image, as shown in  FIG. 4B . A character string “[bow-shape correction]” is displayed in an upper portion of the bow-shape correction adjustment image D 2 . The control point area image CA 2  is enlarged and displayed as an enlarged image Z 2  below the character string. 
     The enlarged image Z 2  has additional triangular direction marks T pointing upward and downward, which indicate that a central portion (that is, control point CP 2 ) of the side displayed in the control point area image CA 2  is movable upward and downward (position is adjustable). Further, a message “Make adjustment” is displayed in a lower portion of the bow-shape correction adjustment image D 2 , prompting the user to adjust the position of the control point CP 2  on the side. In the state in which the bow-shape correction adjustment image D 2  is displayed, the user can adjust the position of the control point CP 2  (central portion of side) by operating the direction keys. When the position of the control point CP 2  is changed, the projected image A 3  is corrected to a bow-shaped image based on the position of the control point CP 2  (curved distortion correction). 
     The following other character strings representing what the user can do are displayed in a lower portion of the bow-shape correction adjustment image D 2 : adjust the bow-shape correction by operating the upward and downward direction keys; and terminate the adjustment and return to the control point area selection image N 1  by operating the enter key or the ESC key. It is noted that the range within which the position of the control point CP 2  is adjusted by operating the direction keys is within the pixel region of each of the liquid crystal light valves  12 R,  12 G, and  12 B and, in the present embodiment, along the line connecting the center of the side of the contour of the input image to the center of the pixel region, that is, the center of the image. 
     The description has been made with reference to the bow-shape correction adjustment images D 1  and D 2 . Substantially the same thing holds true for bow-shape correction adjustment images D corresponding to the control point area images CA 3  to CA 8 , and the positions of the control points CP 3  to CP 8  are adjustable. As in the case of the control point CP 2 , the range within which the position of each of the control points CP 4 , CP 5 , and CP 7  is adjusted is within the pixel region of each of the liquid crystal light valves  12 R,  12 G, and  12 B and along the line connecting the center of the side of the contour of the input image to the center of the pixel region. 
     A description will next be made of processes that the projector  1  carries out to perform the bow-shape correction (curved distortion correction). 
       FIG. 5  is a flowchart of processes that the projector  1  according to the present embodiment carries out to perform the bow-shape correction. 
     When the bow-shape correction is selected in the menu image M 1 , the control unit  20  instructs the OSD processing unit  32  to display the control point area selection image N (step S 101 ). The control unit  20  then determines whether or not any of the control point area images CA (that is, any of the control points CP) has been selected (step S 102 ). The control unit  20  and the OSD processing unit  32  in this process correspond to a selection unit and a control point selection unit, and the operation of the projector  1  in this process corresponds to a selection step and a control point selection step. When any of the control point area images CA is selected (step S 102 : YES), the control unit  20  instructs the OSD processing unit  32  to display the bow-shape correction adjustment image D corresponding to the selected control point area image CA (step S 103 ). 
     The control unit  20  determines whether or not any of the direction keys has been operated for adjustment (step S 104 ). When any of the direction keys has been operated for adjustment (step S 104 : YES), the control unit  20  instructs the image correction unit  33  to form an image formation region based on the position of the adjusted control point CP (step S 105 ). The control unit  20  that moves the control point CP for adjustment corresponds to a control point movement unit, and the operation of the control unit  20  corresponds to a movement step. In this process, the image correction unit  33  forms an image formation region, that is, the image contour in such away that the adjusted control point CP is connected to adjacent control points CP with a bow-shape curve. The operation of the image correction unit  33  corresponds to a correction step. 
     The image correction unit  33  corrects the image information to fit in the image formation region (step S 106 ). The image correction unit  33  that corrects image information corresponds to an image correction unit. The control unit  20  then returns to step S 103 . 
     When no direction key has been operated for adjustment (step S 104 : NO), the control unit  20  determines whether or not the ESC key has been pressed (step S 107 ). When the ESC key has not been pressed, the control unit  20  returns to step S 103 . When the ESC key has been pressed (step S 107 : YES), the control unit  20  returns to step S 101 . 
     When no control point area has been selected (step S 102 : NO), the control unit  20  determines whether or not the ESC key has been pressed (step S 108 ). When the ESC key has not been pressed (step S 108 : NO), the control unit  20  returns to step S 101 . When the ESC key has been pressed (step S 108 : YES), the control unit  20  instructs the OSD processing unit  32  to stop displaying the control point area selection image N 1  (step S 109 ). The bow-shape correction is then terminated. 
     A description will next be made of an image having undergone the bow-shape correction described above. 
       FIG. 6  is a plan view showing a pixel region having undergone the bow-shape correction. 
       FIG. 6  shows a state in which the control point area images CA 2  and CA 7  (that is, control points CP 2  and CP 7 ) have undergone the bow-shape correction; an image formation region H having a pincushion distorted shape has been formed in a pixel region P; and image information has been corrected. Regions S 1  and S 2  outside the image formation region H in the pixel region P are blackened (light hardly passes through regions S 1  and S 2 ). After the bow-shape correction described above is made, the projector  1  outputs a distorted image having a pincushion shape and corrected to fit in the image formation region H. For example, when the projection surface S is concavely curved, the user projects an image on the concave projection surface S while performing the bow-shape correction (curved distortion correction). The distorted projected image having the pincushion shape can thus correct the curved distortion on the projection surface S and provide a rectangular shape. 
     Although not shown, a distorted image formation region H having a barrel shape can also be formed in the pixel region P. Specifically, a barrel-shaped image formation region H can be formed by performing inward bow-shape correction with respect to the pixel region P on the control point area images CA 1 , CA 3 , CA 6 , and CA 8 . The image information is thus corrected to fit in the barrel-shaped image formation region H. When the projection surface S is convexly curved, curved distortion on the projection surface Scan be corrected by projecting a barrel-shaped image from the projector  1 . 
     The first embodiment provides the following advantageous effects. 
     (1) The projector  1  displays the control point area selection image N 1  and allows the user to select any of the control point area images CA (that is, any of the control points CP). The projector  1  displays a bow-shape correction adjustment image D corresponding to the selected control point area image CA. The user can adjust the position of the control point CP in the pixel region P. The image correction unit  33  in the projector  1  then forms an image formation region H in such a way that the contour thereof passes through the adjusted control point CP. Further, the image correction unit  33  corrects image information to fit in the image formation region H. The user can thus correct the shape of a projected image by operating the direction keys provided on the operation reception unit  22  or the remote control  24  to move the control point CP while viewing the projected image. That is, the user can readily correct the shape of the projected image without any prior knowledge. Further, since the geometric shape of a projected image can be corrected by using the projector  1  alone, the convenience of the user is improved. 
     (2) The image correction unit  33  in the projector  1  forms an image formation region H by connecting the adjusted control point CP to adjacent control points CP with a bow-shaped curve. As a result, the image formation region H has a shape including the curve, and the image information corrected by the image correction unit  33  represents an image having a curved contour. Projecting the thus formed image having a curved contour can cancel curved distortion on the projection surface S that is curved. 
     (3) In the projector  1 , the control point CP is placed at each of the four vertices (corners) of the contour of an image based on image information and at a point on each of the four sides of the contour. The thus set eight control points (CP 1  to CP 8 ) allow the user to form an image formation region H and operate the projector  1  in a simple, effective manner. 
     (4) In the projector  1 , default positions of the control points CP on the four sides (CP 2 , CP 4 , CP 5 , and CP 7 ) are the centers of the respective sides of the contour of an image. The user can therefore adjust the control points CP by using the direction keys, that is, form an image formation region H in a well balanced manner. 
     (5) In the projector  1 , each of the control points CP on the four sides (CP 2 , CP 4 , CP 5 , and CP 7 ) can be adjusted along the line connecting the default position to the center of the pixel region. The formation of an image formation region H, correction of image information, and other software processing can therefore be simplified. 
     The invention is not limited to the first embodiment, and a variety of changes, improvements, and other modifications can be made thereto. Variations of the first embodiment will be described below. 
     Variation 1 
     In the embodiment described above, eight control points CP (CP 1  to CP 8 ) are provided, but the number of control points CP is not limited to eight. For example, when the number of control points CP is greater than eight, more precise correction can be made. 
     Variation 2 
     In the embodiment described above, the default positions of the control points CP on the sides (CP 2 , CP 4 , CP 5 , and CP 7 ) of the contour of an image based on image information are centers of the sides, but the default positions are not limited to the centers. 
     Variation 3 
     In the embodiment described above, each of the control points CP 2 , CP 4 , CP 5 , and CP 7  on the sides is adjusted along the line connecting the center of the side to the center of the pixel region, but the adjustment is not necessarily made this way. The control points CP 2 , CP 4 , CP 5 , and CP 7  may alternatively be adjustable obliquely. 
     Variation 4 
     In the embodiment described above, the light source apparatus  11  includes the discharge-type light source lamp  11   a , but an LED (light emitting diode) light source, a laser, and other solid-state light sources, and other suitable light sources can be used. 
     Variation 5 
     In the embodiment described above, the projector  1  uses the transmissive liquid crystal light valves  12 R,  12 G, and  12 B as the light modulators, but reflective liquid crystal light valves and other reflective light modulators can be used. Further, a micromirror array device that modulates light emitted from a light source by controlling the direction of light incident on each micromirror as a pixel and other similar devices can be used. 
     Second Embodiment 
     A second embodiment to which the invention is applied will next be described. In the second embodiment, trapezoidal distortion of an image projected on the projection surface S and distortion called pincushion distortion, barrel distortion, or otherwise named are corrected. 
       FIG. 7  is a block diagram showing a schematic configuration of a projector  2  according to the second embodiment. 
     The projector  2  shown in  FIG. 7  includes an image projection unit  10 , a control unit  20 , a storage unit  41 , an input operation unit  42 , an image information input unit  30 , an image processing unit  31 , an OSD processing unit  32 , and an image correction unit  33 . In the second embodiment, components common to those in the first embodiment have the same names and reference characters, and no description thereof will therefore be made. 
     In the image projection unit  10 , which corresponds to a display unit according to the invention, light outputted from the light source apparatus  11  is modulated by the liquid crystal light valves  12  to form an image (image light), and the image is enlarged and projected by the projection lens  13  and displayed on the projection surface S, as in the image projection unit  10  in the projector  1  described above. 
     As described above, each of the liquid crystal light valves  12  is formed, for example, of a liquid crystal panel having a liquid crystal material sealed between a pair of transparent substrates. Each of the liquid crystal light valves  12  has a rectangular pixel region  12   a  formed of a plurality of pixels  12   p  arranged in a matrix and can apply a drive voltage to the liquid crystal material for each of the pixels  12   p . When the liquid crystal driver  14  applies a drive voltage according to inputted image information to each of the pixels  12   p , the pixel  12   p  sets its optical transmittance at a value according to the image information. As a result, the light outputted from the light source apparatus  11  is modulated when passing through the image regions  12   a  of the liquid crystal light valves  12  to form color images according to the image information. 
     The thus formed color images are combined for each of the pixels  12   p  by a light combining system (not shown) into a single color image, which is then enlarged and projected by the projection lens  13  on the projection surface S. The projection lens  13  has a zoom mechanism (not shown) for changing a factor according to which an image is magnified, and the user can adjust the size of a displayed image by using the zoom mechanism. 
     In the present specification, the entirety of an image projected through the projection lens  13  is called a “projected image.” A projected image is produced by projecting an image formed across the entire pixel region  12   a , and even when the entirety or part of the pixel region  12   a  is blackened (light hardly passes therethrough), the whole range including the portion corresponding to the blackened region is a projected image. Further, for example, when an image is projected toward the screen, and even when part of the image lies offscreen and is projected, for example, on a wall behind the screen, the whole range including the offscreen portion is a projected image. 
     In the present embodiment, the control unit  20  is connected to the storage unit  41 , which stores, for example, a control program, and operates in accordance with the control program stored in the storage unit  41  to oversee the control of the operation of the projector  2 . That is, the control unit  20  along with the storage unit  41  functions as a computer. 
     The storage unit  41  is formed of a mask ROM (read only memory), a flash memory, an FeRAM (ferroelectric RAM), or any other nonvolatile memory. The storage unit  41  stores, for example, the control program for controlling the operation of the projector  2  and a variety of setting data that define operation conditions and other parameters under which the projector  2  operates. 
     The input operation unit  42 , which has the same function as that of the operation reception unit  22  described above and receives user&#39;s input operation, includes a plurality of operation keys that allow the user to issue a variety of instructions to the projector  2 . The operation keys provided on the input operation unit  42  include a power key for turning on and off a power supply, a menu key for displaying a menu image for a variety of settings, an enter key for accepting an item selected, for example, in the menu image, four directional keys corresponding to the upward, downward, rightward, and leftward directions, and a cancel key for instructing to cancel or otherwise deselect operation. The input operation unit  42  in the present embodiment further includes a pincushion distortion correction key for correcting pincushion distortion and a trapezoidal distortion correction key for correcting trapezoidal distortion. When the user operates any of the variety of operation keys on the input operation unit  42 , the input operation unit  42  outputs an operation signal according to the user&#39;s operation to the control unit  20 . The input operation unit  42  may alternatively be a remote control (not shown) that allows remote operation. In this case, the remote control sends an infrared operation signal according to user&#39;s operation, and a remote control signal receiver (not shown) receives the operation signal and forwards it to the control unit  20 . 
     The image correction unit  33  corrects an image (image information) based on an instruction from the control unit  20 . In the second embodiment, the image correction unit  33  sets an image formation region  12   e  having a shape set by the user in the pixel region  12   a  of each of the liquid crystal light valves  12  (see  FIG. 9C ). Image information inputted from the OSD processing unit  32  is so corrected that an input image Pi is formed in the image formation region  12   e . Further, the image correction unit  33  sets each pixel  12   p  outside the image formation region  12   e  at a black pixel value, that is, a pixel value that minimizes optical transmittance in order to disable the region outside the image formation region  12   e . The image correction unit  33  outputs the thus corrected image information to the liquid crystal driver  14 . When the control unit  20  does not instruct image correction, the image correction unit  33  does not process the image information inputted from the OSD processing unit  32  but directly outputs it to the liquid crystal driver  14 . In this case, the input image Pi is formed across the entire pixel region  12   a . In other words, the entirety of the pixel region  12   a  is the image formation region  12   e.    
     A description will next be made of a summary of trapezoidal distortion correction performed by the projector  2 . 
       FIGS. 8A and 8B  and  FIGS. 9A to 9D  describe trapezoidal distortion.  FIGS. 8A and 9A  are side views of the projector  2  and the projection surface S viewed sideways.  FIGS. 8B, 9B, and 9D  are front views showing the projection surface S.  FIG. 9C  shows the pixel region  12   a  of each of the liquid crystal light valves  12 . 
     In a state in which the projector  2  is not inclined to the projection surface S, that is, in a state in which the optical axis of the projection lens  13  is oriented in substantially the same direction as a normal to the projection surface S as shown in  FIG. 8A , a projected image Ao is accompanied by no trapezoidal distortion and displayed in a normal (rectangular) shape, as shown in  FIG. 8B . In this case, since an input image Pi only needs to be formed across the entire pixel region  12   a , the image correction unit  33  need to make no correction, and zoom adjustment, adjustment of the position where the projector  2  is installed, and other adjustment may be so made as appropriate that the projected image Ao (input image Pi) is displayed across the entire projection surface S. 
     On the other hand, in a state in which the projector  2  is inclined to the projection surface S, that is, in a state in which the optical axis of the projection lens  13  is oriented in a direction different from the direction of a normal to the projection surface S as shown in  FIG. 9A , a projected image Ao is accompanied by trapezoidal distortion as shown in  FIG. 9B . As a result, a displayed input image Pi, when formed across the entire pixel region  12   a , is distorted by trapezoidal distortion. To address the problem, an image formation region  12   e  having a shape capable of canceling the trapezoidal distortion, that is, a shape distorted oppositely to the projected image Ao, is set in the pixel region  12   a , as shown in  FIG. 9C , and the input image Pi is formed in the thus set image formation region  12   e . In this way, the distorted shape of the image formation region  12   e  (input image Pi) is canceled by the trapezoidal distortion, whereby the input image Pi displayed on the projection surface S shows the original (rectangular) shape with the trapezoidal distortion corrected (see  FIG. 9D ). 
     As described above, since the input operation unit  42  includes the trapezoidal distortion correction key, the user can operate the trapezoidal distortion correction key to set the shape of the image formation region  12   e.    
     Further, when the projection surface S is curved, distortion called pincushion distortion, barrel distortion, or otherwise named (hereinafter referred to as pincushion distortion) occurs. 
       FIGS. 10A to 10H  describe pincushion distortion.  FIG. 10A  is a perspective view of the projector and the projection surface viewed obliquely downward.  FIGS. 10B, 10D, 10F, and 10H  show the pixel region of one of the liquid crystal light valves.  FIGS. 10C, 10E, and 10G  are front views showing the projection surface. 
     In  FIG. 10A , which shows a state in which the projector is installed in front of the projection surface S, no trapezoidal distortion occurs but a projected image Ao is accompanied by distortion that convexly curves the upper and lower sides of a projected image Ao because the projection surface S is curved. When an input image Pi is formed across the entire pixel region  12   a , the displayed input image Pi, which is displayed as a rectangular image if the projection surface S is flat, is distorted by pincushion distortion. 
     In the example shown in  FIG. 10A , the projection surface S is not distorted in the up-down direction, that is, the vertical direction but is (cylindrically) curved to form a convex shape whose center in the right-left direction, that is, the horizontal direction separates away from the projector  2 . In this case, the projected image Ao is accompanied by barrel distortion that curves the upper and lower lines. 
     To address the problem, an image formation region  12   e  having a shape capable of canceling the pincushion distortion, that is, a shape distorted oppositely to the projected image Ao is set in the pixel region  12   a , as shown in  FIG. 10B , and the input image Pi is formed in the thus set image formation region  12   e . The distorted shape of the image formation region  12   e  (input image Pi) is canceled by the pincushion distortion, whereby the input image Pi is displayed on the projection surface S in the original (rectangular) shape with the pincushion distortion corrected, as in the state shown in  FIG. 9D . 
     Further, when the projector  2  is installed as shown in  FIG. 10A  and inclined to the projection surface S as shown in  FIG. 9A , both the trapezoidal distortion shown in  FIG. 9B  and the pincushion distortion shown in  FIG. 10A  occur. In this case, a projected image Ao is distorted by the trapezoidal distortion and the pincushion distortion, for example, into a barrel shape having a widened upper portion. In this case, the shape of the image formation region  12   e  formed in the pixel region  12   a  is first so deformed that one of the trapezoidal distortion and the pincushion distortion is corrected and then so deformed that the other distortion is corrected. A rectangular projected image Ao can thus be displayed on the projection surface S. 
       FIG. 10C  shows a case where the projection surface S is a cylindrical surface convex toward the projector  2 . In this case, a projected image Ao is accompanied by pincushion distortion opposite to that shown in  FIG. 10A . To correct the distortion, an image formation region  12   e  having a shape distorted oppositely to the projected image Ao is set in the pixel region  12   a , as shown in  FIG. 10D . The pincushion distortion can be canceled, and a rectangular input image Pi can be displayed on the projection surface S. 
       FIG. 10E  shows a case where the projection surface S is a cylindrical surface that is not distorted in the horizontal direction but is distorted in the vertical direction and has a convex shape that separates away from the projector  2 . In this case, a projected image Ao projected on the projection surface S is so distorted that the right and left vertical sides are curved. To correct the distortion, an image formation region  12   e  having a shape distorted oppositely to the projected image Ao is set in the pixel region  12   a , as shown in  FIG. 10F . The pincushion distortion can be canceled, and a rectangular input image Pi can be displayed on the projection surface S. 
       FIG. 10G  shows a case where the projection surface S is a cylindrical surface that is not distorted in the horizontal direction but is distorted in the vertical direction and the projection surface S is convex toward the projector  2 , which is opposite to  FIG. 10E . In this case, a projected image Ao projected on the projection surface S is so distorted that the right and left vertical sides are curved. To correct the distortion, an image formation region  12   e  having a shape distorted oppositely to the projected image Ao is set in the pixel region  12   a , as shown in  FIG. 10H . The pincushion distortion can be canceled, and a rectangular input image Pi can be displayed on the projection surface S. 
     In a case where the projection surface S is a more complicated surface, such as an elliptically curved surface and a parabolic surface, as well as in the surfaces shown in  FIGS. 10A, 10C, 10E, and 10G , a rectangular projected image Ao can be displayed by forming an image formation region  12   e  that cancels pincushion distortion produced by the curved surface in the pixel region  12   a.    
     As described above, since the input operation unit  42  includes the pincushion distortion correction key, the user can operate the pincushion distortion correction key to set the shape of the image formation region  12   e  for pincushion distortion correction. 
       FIG. 11  is a flowchart for describing the operation of the projector  2  when the trapezoidal distortion correction key or the pincushion distortion correction key is operated. In the operation shown in  FIG. 11  and  FIG. 12 , which will be described later, the control unit  20  cooperates with the OSD processing unit  32  and functions as an identification image display unit and an enhancement display unit, and the input operation unit functions as a selection operation unit and a movement operation unit under the control of the control unit  20 . The selection operation unit and the movement operation unit correspond to the selection unit. 
     In a state in which the projector  2  projects an input image Pi, and when the user operates the trapezoidal distortion correction key or the pincushion distortion correction key, the control unit  20  operates in accordance with the procedure shown in  FIG. 11 . The input operation unit  42  may alternatively be provided with a distortion correction key corresponding to both the pincushion distortion correction and the trapezoidal distortion correction. In this case, a menu screen that allows the user to choose the pincushion distortion correction or the trapezoidal distortion correction is displayed by the projector  2  in response to user&#39;s operation of the distortion correction key, and the pincushion distortion correction or the trapezoidal distortion correction is chosen on the menu screen by operating the input operation unit  42 . In this configuration, only one distortion correction operation key is required on the input operation unit  42 , and the user only needs to operate the distortion correction key instinctively without identifying the type of distortion when it is difficult to identify the distortion of a projected image Ao on the projection surface S to be trapezoidal distortion or pincushion distortion or when a combination of trapezoidal distortion and pincushion distortion occurs, whereby the operability of the projector can be improved. 
     As shown in  FIG. 11 , the control unit  20  determines in step S 201  which correction the user has instructed to make by key operation through the input operation unit  42 , pincushion distortion correction or trapezoidal distortion correction. When the user instructs to make pincushion distortion correction, the control unit  20  starts a pincushion distortion correction mode and makes pincushion distortion correction, which will be described later, in step S 202 . The control unit  20  then terminates the procedure. 
     When the user instructs to make trapezoidal distortion correction, the control unit  20  proceeds to step S 203 , where the control unit  20  starts a trapezoidal distortion correction mode and makes the trapezoidal distortion correction. The control unit  20  then instructs the OSD processing unit  32  in step S 204  to display an input image Pi with a corner selection image Ps (see  FIG. 13A ) overlaid thereon. Steps S 202  to S 210  correspond to the selection step. 
       FIGS. 13A and 13B  show images displayed when the trapezoidal distortion correction is in progress.  FIG. 13A  shows the corner selection image Ps, and  FIG. 13B  shows a corner adjustment image Pz. 
     The corner selection image Ps has a title section Ta, four identification images C corresponding to the four corners of an input image Pi, that is, the four corners of an image formation region  12   e , a message section Ma where a message for the user is displayed, and a key guide section Ka that guides the user to operable operation keys and the operation thereof. 
     The four identification images C are formed of an identification image C 1  corresponding to the upper left corner of the image formation region  12   e  (input image Pi), an identification image C 2  corresponding to the upper right corner, an identification image C 3  corresponding to the lower left corner, and an identification image C 4  corresponding to the lower right corner, and they all have the same size. The identification images C 1  to C 4  are arranged in a matrix formed of two rows by two columns and disposed in the matrix in the corresponding positions (for example, the identification image C 1  corresponding to the upper left corner is disposed in an upper left portion of the matrix). Each of the identification images C 1  to C 4  has an illustration representing the corresponding corner drawn therein. 
     The title section Ta displays “Corner position adjustment,” which clearly shows the user that the function intends to correct trapezoidal distortion by adjusting the position of any of the corners. The message section Ma displays “Select area,” prompting the user to select one of the corners by selecting one of the identification images C 1  to C 4 . The selected one (identification image C 1  in the example shown in  FIG. 13A ) of the identification images C 1  to C 4  is colored differently from the other three, which shows that the differently colored identification image C has been selected. In the following sections, the color of an identification image C that has been selected is also called a “selected state color,” and the color of identification images C that have not been selected is also called an “unselected state color.” The user can select a desired identification image C by operating the direction keys, and the selection of an identification image C is accepted by operating the enter key after the identification image C is selected. 
     The corner adjustment image Pz has a title section Tb, an enlarged image display section Z, a message section Mb where a message for the user is displayed, and a key guide section Kb that guides the user to operable operation keys and the operation thereof, as shown in  FIG. 13B . The title section Tb displays “Corner position adjustment,” as the title section Ta in the corner selection image Ps does. 
     The enlarged image display section Z displays an enlarged identification image C (identification image C 1  in the example shown in  FIG. 13B ) selected from the four identification images C 1  to C 4  described above in the corner selection image Ps but does not display the unselected three identification images C. The enlarged image display section Z also has additional triangular direction marks E pointing upward, downward, rightward, and leftward, which indicate that the corner corresponding to the enlarged identification image C is movable upward, downward, rightward, and leftward (position is adjustable). The message section Mb displays “Make adjustment,” prompting the user to adjust the position of the corner. In the state in which the corner adjustment image Pz is displayed, the user can adjust the position of the corner by operating the direction keys. 
     In step S 205  in  FIG. 11 , the control unit  20  determines whether or not the user has operated any of the direction keys. When no direction key has been operated, the control unit  20  proceeds to step S 207 , whereas when any of the direction keys has been operated, the control unit  20  proceeds to step S 206 . 
     In step S 206 , the control unit  20  newly selects one of the other identification images C located in the direction specified by the operated direction key, and the control unit  20  returns to step S 204 . At this point, in the corner selection image Ps, the newly selected identification image Cis displayed in the selected state color, whereas the previously selected identification image C is displayed in the unselected state color. 
     In step S 207 , the control unit  20  determines whether or not the user has operated the enter key. When the enter key has not been operated, the control unit  20  proceeds to step S 208 , whereas when the enter key has been operated, the control unit  20  proceeds to step S 210 . 
     In step S 208 , the control unit  20  determines whether or not the user has operated the cancel key. When the cancel key has not been operated, the control unit  20  returns to step S 205 , whereas when the cancel key has been operated, the control unit  20  proceeds to step S 209 . 
     In step S 209 , the control unit  20  instructs the OSD processing unit  32  to terminate the overlay display of the corner selection image Ps and terminates the procedure. 
     In step S 210 , the control unit  20  instructs the OSD processing unit  32  to display the corner adjustment image Pz (see  FIG. 13B ) as an overlaid image instead of the corner selection image Ps. 
     The control unit  20  subsequently determines in step S 211  whether or not any of the direction keys has been operated. When any of the direction keys has been operated, the control unit  20  proceeds to step S 212 , whereas when no direction key has been operated, the control unit  20  proceeds to step S 213 . 
     In step S 212 , the control unit  20  instructs the image correction unit  33  to move the selected corner in the direction specified by the operated direction key, and the control unit  20  returns to step S 210 . The operation corresponds to the movement step. For example, when the identification image C 1  is selected, that is, the upper left corner is selected in the corner selection image Ps, the image correction unit  33  sets the upper left corner of the image formation region  12   e  as an object to be moved and moves the upper left corner by a predetermined amount in the direction specified by the operated direction key, as shown in  FIGS. 14A to 141 . Thereafter, the image correction unit  33  corrects the image information in such a way that the input image Pi is formed in the image formation region  12   e  newly shaped by moving the corner. When the user repeatedly operates any of the direction keys or presses any of the direction keys for a long time, steps S 211  and S 212  are repeatedly carried out, and the selected corner can be moved by a necessary amount. 
     It is noted that the upward, downward, rightward, and leftward directions of a projected input image Pi do not necessarily agree with the upward, downward, rightward, and leftward directions of the liquid crystal light valves  12 . In this case, a corner of an image formation region  12   e  is so moved that a corner of the projected input image Pi is moved in a direction according to user&#39;s operation. 
     Further, since each of the corners of an image formation region  12   e  is unable to move out of the pixel region  12   a , when any of the corners is located on the outer edge (boundary) of the pixel region  12   a , that is, reaches the limit of the movable range, the control unit  20  ignores operation of the direction key that moves the corner out of the pixel region  12   a . Further, when any of the corners is located on the outer edge of the pixel region  12   a , the control unit  20  notifies the user that the corner is unable to move outward by instructing the OSD processing unit  32  to change the color of the direction mark E that causes the corner to move out of the pixel region  12   a , that is, the direction mark E pointing in the direction in which the corner is unable to move to a color less visible (gray or any other dark color, for example) than the color of the direction marks E pointing in the other directions (orange or any other bright color, for example). For example, when a corner to be moved is located at the upper end of the pixel region  12   a  as shown in  FIGS. 14A, 14B, and 14C , the upward direction mark E is displayed in the less visible color, and when the upward direction key is operated, the operation is ignored. When a corner to be moved is located at the left end of the pixel region  12   a  as shown in  FIGS. 14A, 14D, and 14G , the leftward direction mark E is displayed in the less visible color, and when the leftward direction key is operated, the operation is ignored. The reason why the control unit  20  returns to step S 210  after step S 212  and newly displays the corner adjustment image Pz again is to update the colors of the direction marks E in accordance with the situations. The limit of the movable range is not necessarily the outer edge of the pixel region  12   a  but may be set arbitrarily within the pixel region  12   a.    
     In step S 213  in  FIG. 11 , the control unit  20  determines whether or not the enter key or the cancel key has been operated. When no enter key or cancel key has been operated, the control unit  20  returns to step S 211 . On the other hand, when the enter key or the cancel key has been operated, the control unit  20  completes moving the selected corner and returns to step S 204 , where the control unit  20  restores the state in which the corner selection image Ps is displayed. The user may then select any of the other corners to continue the adjustment or operate the cancel key to terminate the procedure. 
     The image correction unit  33  then deforms the projected image Ao on the projection surface S by producing deformed image formation region  12   e  on each of the liquid crystal light valves  12  as illustrated in  FIGS. 14A to 141  and forming an input image Pi in the image formation region  12   e . The trapezoidal distortion, for example, that shown in  FIGS. 9A to 9D , is thus corrected. In the operation described above, the image correction unit  33  functions as a correction unit, and the operation thereof corresponds to the correction step. The projector  2  can thus display the corner selection image Ps and the corner adjustment image Pz in accordance with the operation of the trapezoidal distortion correction key, the direction keys, the enter key, and the cancel key for trapezoidal distortion correction. 
       FIG. 12  is a detailed flowchart showing the pincushion distortion correction carried out in step S 202  ( FIG. 11 ). 
     When the user instructs to make pincushion distortion correction, the control unit  20  instructs the OSD processing unit  32  in step S 221  to display an input image Pi with an adjustment section selection image Pu overlaid thereon. 
       FIGS. 15 to 17  show images displayed when the pincushion distortion correction is in progress.  FIG. 15  shows the adjustment section selection image Pu.  FIG. 16  shows a corner adjustment image Pv.  FIG. 17  shows a side adjustment image Pw. 
     The adjustment section selection image Pu has a title section Tc, four identification images G 1  to G 4  corresponding to the four corners of an input image Pi, that is, the four corners of an image formation region  12   e , four identification images G 5  to G 8  corresponding to the four sides of the image formation region  12   e , a message section Mc where a message for the user is displayed, and a key guide section Kc that guides the user to operable operation keys and the operation thereof. 
     The identification images G 1  to G 8  are formed of an identification image G 1  corresponding to the upper left corner of the image formation region  12   e  (input image Pi), an identification image G 2  corresponding to the upper right corner, an identification image G 3  corresponding to the lower left corner, an identification image G 4  corresponding to the lower right corner, G 5  corresponding to the upper side, G 6  corresponding to the left side, G 7  corresponding to the right side, and G 8  corresponding to the lower side, and they all have the same size. The identification images G 1  to G 8  are arranged in a matrix formed of three rows by three columns and having a central space and disposed in the matrix in the corresponding positions in the image formation region  12   e . For example, the identification image G 1  corresponding to the upper left corner is disposed in an upper left portion of the matrix. Each of the identification images G 1  to G 8  has an illustration representing the corresponding corner or side drawn therein, whereby the user can intuitively understand the relationship between the corners and sides of the image formation region  12   e  and the identification images G 1  to G 8 . 
     The title section Tc displays “Pincushion distortion correction,” which clearly shows the user that the function intends to correct pincushion distortion, and the message section Mc displays “Select area,” prompting the user to select one of the corners and the sides by selecting one of the identification images G 1  to G 8 . The selected one (identification image G 1  in the example shown in  FIG. 15 ) of the identification images G 1  to G 8  is surrounded by a frame colored differently from those surrounding the other seven, which shows that the identification image G surrounded by the differently colored frame has been selected. In the following sections, the color for an identification image G that has been selected is also called a “selected state color,” and the color for identification images G that have not been selected is also called an “unselected state color.” The user can select a desired identification image G by operating the direction keys, and the selection of an identification image G is accepted by operating the enter key after the identification image G is selected. 
     The corner adjustment image Pv has a title section Td, an enlarged image display section V, a message section Md where a message for the user is displayed, and a key guide section Kd that guides the user to operable operation keys and the operation thereof, as shown in  FIG. 16 . The title section Td displays “Pincushion distortion correction,” as the title section Tc in the adjustment section selection image Pu does. The corner adjustment image Pv is displayed when any of the identification images G 1  to G 4  corresponding to the corners is selected in the adjustment section selection image Pu shown in  FIG. 15 . 
     The enlarged image display section V displays an enlarged identification image G (identification image G 1  in the example shown in  FIG. 16 ) selected in the adjustment section selection image Pu but does not display the unselected three identification images G (identification images G 2  to G 4  in the example shown in  FIG. 16 ). The enlarged image display section V also has additional triangular direction marks E pointing upward, downward, rightward, and leftward, which indicate that the corner corresponding to the enlarged identification image G can be movable upward, downward, rightward, and leftward (position is adjustable). The message section Md displays “Make adjustment,” prompting the user to adjust the position of the corner. In the state in which the corner adjustment image Pv is displayed, the user can adjust the position of the corner by operating the direction keys. 
     In the adjustment section selection image Pu ( FIG. 15 ), when any of the identification images G 5  to G 8  corresponding to the sides is selected, the side adjustment image Pw shown in  FIG. 17  is displayed instead of the corner adjustment image Pv. The side adjustment image Pw has a title section Td, an enlarged image display section V, a message section Md where a message for the user is displayed, and a key guide section Kd that guides the user to operable operation keys and the operation thereof, which are the same as those in the corner adjustment image Pv, and the enlarged image display section V displays an enlarged identification image G (identification image G 5  in the example shown in  FIG. 17 ) that corresponds to any of the sides of the image formation region  12   e  and has been selected in the adjustment section selection image Pu. In the side adjustment image Pw, the identification images G corresponding to the three sides that have not been selected (G 6  to G 8  in the example shown in  FIG. 17 ) are not displayed. 
     The enlarged image display section V also has additional triangular direction marks E pointing upward, downward, rightward, and leftward, as the corner adjustment image Pv does. However, since the sides of the image formation region  12   e  are adjustable only in the upward and downward directions or the rightward and leftward directions, two direction marks E pointing in two directions are added to the side adjustment image Pw. When either of the identification images G 5  and G 8  corresponding to the upper and lower sides is selected, two direction marks E pointing upward and downward are added to the side adjustment image Pw, whereas when either of the identification images G 6  and G 7  corresponding to the left and right sides is selected, two direction marks E pointing leftward and rightward are added to the side adjustment image Pw. 
     The direction marks E indicate that a side corresponding to an enlarged identification image G is movable upward and downward or leftward and rightward (position is adjustable). 
       FIGS. 18A to 18I, 19A to 19C, and 20A to 20C  show how an image formation region  12   e  is deformed in accordance with operation performed in the corner adjustment image Pv and the side adjustment image Pw.  FIGS. 18A to 18I  describe movement of a corner of the image formation region  12   e .  FIGS. 19A to 19C and 20A to 20C  each describe movement of a middle point of a side of the image formation region  12   e .  FIGS. 18A to 18I, 19A to 19C , and  20 A to  20 C each show the pixel region  12   a  of one of the liquid crystal light valves  12 . 
       FIGS. 18A to 18I  show examples of operation on the identification image G 1  corresponding to the upper left corner of the image formation region  12   e . When any of the direction keys is operated in the state in which the corner adjustment image Pv is displayed, the image formation region  12   e  is so deformed that the corner corresponding to the identification image G displayed in the enlarged image display section V is moved upward, downward, rightward, or leftward in accordance with the operation, as shown in  FIGS. 18A to 18I . For example, when the upward direction key is operated in the state shown in  FIG. 18E , the corner of the image formation region  12   e  is moved to a position one step upward. In accordance with the movement of the corner, the sides connected to the corner, that is, the curves that form the contour of the image formation region  12   e , are deformed, and the shape of the image formation region  12   e  is changed as shown in  FIG. 18B . The change in the curves in accordance with the movement of the corner is computed in accordance with an algorithm set in advance by the control unit  20 . On the other hand, when the downward direction key is operated in the state shown in  FIG. 18E , the corner of the image formation region  12   e  is moved to a position one step downward and the image formation region  12   e  is deformed as shown in  FIG. 18H . Similarly, when the rightward direction key is operated, the image formation region  12   e  is deformed as shown in  FIG. 18F , whereas when the leftward direction key is operated, the image formation region  12   e  is deformed as shown in  FIG. 18D . As described above, the image formation region  12   e  can be deformed by operating the direction marks E for distortion correction. 
     Further, since each of the corners of the image formation region  12   e  is unable to move out of the pixel region  12   a , when any of the corners is located on the outer edge (boundary) of the image formation region  12   e , that is, reaches the limit of the movable range, the control unit  20  ignores operation of the direction key that moves the corner out of the pixel region  12   a . Further, when any of the corners is located on the outer edge of the pixel region  12   a , the control unit  20  notifies the user that the corner is unable to move outward by instructing the OSD processing unit  32  to change the color of the direction mark E that causes the corner to move out of the pixel region  12   a , that is, the direction mark E pointing in the direction in which the corner is unable to move to a color less visible (gray or any other dark color, for example) than the color of the direction marks E pointing in the other directions (orange or any other bright color, for example). For example, when a corner to be moved is located at the upper end of the pixel region  12   a  as shown in  FIGS. 18A, 18B, and 18C , the upward direction mark E is displayed in the less visible color, and when the upward direction key is operated, the operation is ignored. When a corner to be moved is located at the left end of the pixel region  12   a  as shown in  FIGS. 18A, 18D, and 18G , the leftward direction mark E is displayed in the less visible color, and when the leftward direction key is operated, the operation is ignored. 
     The identification image G 1  illustrated in  FIGS. 18A to 18I  shows a case where each side of the image formation region  12   e  is deformed to be inwardly convex. When pincushion distortion occurs, however, each side of a projected image Ao may be outwardly or inwardly convex with respect to the normal projected image Ao, as shown in  FIGS. 10A to 10H . In view of the fact described above, for example, when the upper side of the image formation region  12   e  is moved further upward from the state shown in  FIG. 18B , the operation does not need to be terminated because the upper side has reached the limit and is unable to go further, but the user may, for example, be guided to operation of reducing the size of the image formation region  12   e  in the pixel region  12   a . Alternatively, the user may be guided to operation of shifting the image formation region  12   e  in the pixel region  12   a  away from the side that has reached the end of the pixel region  12   a . Still alternatively, the control unit  20  may not only guide the user to the operation described above but also may actually reduce the size of the image formation region  12   e  or shift the image formation region  12   e . In this case, the range within which the pincushion distortion correction can be performed on the projected image Ao on the projection surface S is enlarged. 
       FIGS. 19A to 19C  describe movement of the middle point of a horizontal side of an image formation region  12   e  and show operation on the identification image G 5  corresponding to the upper side of the image formation region  12   e  as an example. When any of the direction keys is operated in the state in which the side adjustment image Pw is displayed, the image formation region  12   e  is so deformed that the side corresponding to the identification image G displayed in the enlarged image display section V is moved upward or downward in accordance with the operation, as shown in  FIGS. 19A to 19C . In this process, the entire side is not translated, but the middle point of the side is moved upward or downward and the side is deformed in accordance with the movement of the middle point. The change in the side is determined by computationally drawing a curve that passes through the moved middle point in accordance with an algorithm set in advance by the control unit  20 . For example, when the upward direction key is operated in the state shown in  FIG. 19B , the center of the side of the image formation region  12   e  is moved to a position one step upward. In accordance with the movement, the side, that is, the curve that forms the contour of the image formation region  12   e  is deformed as shown in  FIG. 19A . On the other hand, when the downward direction key is operated in the state shown in  FIG. 19B , the center of the side of the image formation region  12   e  is moved to a position one step downward and the image formation region  12   e  is deformed as shown in  FIG. 19C . In this process, the control unit  20  moves the center of the side as a predetermined point, but a point in another position may alternatively be moved. It is, however, noted that since an image formation region  12   e  typically has a rectangular shape, moving the center of a side is preferable for pincushion distortion correction. 
       FIGS. 20A to 20C  describe movement of the middle point of a vertical side of an image formation region  12   e  and show operation on the identification image G 6  corresponding to the left side of the image formation region  12   e  as an example. When any of the direction keys is operated in the state in which the side adjustment image Pw is displayed, the image formation region  12   e  is so deformed that the side corresponding to the identification image G displayed in the enlarged image display section V is moved leftward or rightward in accordance with the operation, as shown in  FIGS. 20A to 20C . In accordance with the operation of the direction mark E, the entire side is not translated, but the middle point of the side is moved rightward or leftward and the side is deformed in accordance with the movement of the middle point, as in the case described with reference to  FIGS. 19A to 19C . The change in the side is determined by computationally drawing a curve that passes through the moved middle point in accordance with an algorithm set in advance by the control unit  20 . 
     For example, when the leftward direction key is operated in the state shown in  FIG. 20B , the center of the side of the image formation region  12   e  is moved to a position one step leftward. In accordance with the movement, the side, that is, the curve that forms the contour of the image formation region  12   e  is deformed as shown in  FIG. 20A . On the other hand, when the rightward direction key is operated in the state shown in  FIG. 20B , the center of the side of the image formation region  12   e  is moved to a position one step rightward and the image formation region  12   e  is deformed as shown in  FIG. 20C . 
     In step S 222  in  FIG. 12 , the control unit  20  determines whether or not the user has operated any of the direction keys. When no direction key has been operated, the control unit  20  proceeds to step S 224 , whereas when any of the direction keys has been operated, the control unit  20  proceeds to step S 223 . 
     In step S 223 , the control unit  20  newly selects one of the other identification images G that is located in the direction specified by the operated direction key, and the control unit  20  returns to step S 221 . At this point, in the adjustment section selection image Pu, the newly selected identification image G is displayed in the selected state color, whereas the previously selected identification image G is displayed in the unselected state color. 
     In step S 224 , the control unit  20  determines whether or not the user has operated the enter key. When the enter key has not been operated, the control unit  20  proceeds to step S 225 , whereas when the enter key has been operated, the control unit  20  proceeds to step S 227 . 
     In step S 225 , the control unit  20  determines whether or not the user has operated the cancel key. When the cancel key has not been operated, the control unit  20  returns to step S 222 , whereas when the cancel key has been operated, the control unit  20  proceeds to step S 226 . 
     In step S 226 , the control unit  20  instructs the OSD processing unit  32  to terminate the overlay display of the adjustment section selection image Pu and terminates the procedure. 
     In step S 227 , the control unit  20  instructs the OSD processing unit  32  to overlay the corner adjustment image Pv or the side adjustment image Pw instead of the adjustment section selection image Pu and display the resultant image. Which is displayed, the corner adjustment image Pv or the side adjustment image Pw, is determined by the control unit  20  in accordance with the operation in step S 222 . 
     The control unit  20  subsequently determines whether or not any of the direction keys has been operated in step S 228 . When any of the direction keys has been operated, the control unit  20  proceeds to step S 229 , whereas when no direction key has been operated, the control unit  20  proceeds to step S 230 . 
     In step S 229 , the control unit  20  instructs the image correction unit  33  to move the corner or the side enlarged and displayed in the corner adjustment image Pv or the side adjustment image Pw in the direction specified by the operated direction key, and the control unit  20  returns to step S 227 . The image correction unit  33  moves the corner or the center of the side of the image formation region  12   e  by a predetermined amount in the direction specified by the operated direction key, as described with reference to  FIGS. 18A to 18I, 19A to 19C, and 20A to 20C . Thereafter, the image correction unit  33  corrects the image information in such a way that the input image Pi is formed in the image formation region  12   e  newly shaped by moving the corner or the center of the side. When the user repeatedly operates any of the direction keys or presses any of the direction keys for a long time, steps S 228  and S 229  are repeatedly carried out, whereby the selected corner or side can be moved by a necessary amount. 
     It is noted that the upward, downward, rightward, and leftward directions of a projected input image Pi do not necessarily agree with the upward, downward, rightward, and leftward directions of the liquid crystal light valves  12 . In this case, a corner of an image formation region  12   e  is so moved that a corner of the projected input image Pi is moved in the direction according to user&#39;s operation. 
     The reason why the control unit  20  returns to step S 227  after step S 229  and newly displays the corner adjustment image Pv again is to update the colors of the direction marks E in accordance with the situations. Further, the limit of the movable range of a corner or a side is not necessarily the outer edge of the pixel region  12   a  but may be set arbitrarily within the pixel region  12   a.    
     In step S 230 , the control unit  20  determines whether or not the enter key or the cancel key has been operated. When no enter key or cancel key has been operated, the control unit  20  returns to step S 228 . On the other hand, when the enter key or the cancel key has been operated, the control unit  20  completes moving the selected corner and returns to step S 221 , where the control unit  20  restores the state in which the adjustment section selection image Pu is displayed. The user may then select any of the other corners to continue the adjustment or operate the cancel key to terminate the procedure. 
     A description will next be made of a specific procedure of correcting the pincushion distortion shown in  FIGS. 10A to 10H  in accordance with the flowchart described above. 
       FIGS. 21A to 21G  and  FIGS. 22A and 22B  describe the procedure of correcting the pincushion distortion.  FIGS. 21A  to  21 G are front views showing the projection surface S, and  FIGS. 22A and 22B  show the pixel region  12   a  of one of the liquid crystal light valves  12 . 
     In the state in which an input image Pi projected on the projection surface S is accompanied by pincushion distortion, when the user operates the pincushion distortion correction key, the control unit  20  starts the operation according to the flowchart shown in  FIG. 12 , first overlays the adjustment section selection image Pu on the input image Pi, and displays the resultant image (step S 221 ), as shown in  FIG. 21A . 
     The user operates the direction keys as required (step S 222 ) and first selects the identification image G 1  corresponding to the upper left corner (step S 223 ). When the user then operates the enter key (step S 224 ), the control unit  20  displays the input image Pi with the corner adjustment image Pv overlaid thereon (step S 227 ) and enlarges and displays the identification image G 1  in the enlarged image display section V of the corner adjustment image Pv, as shown in  FIG. 21B . 
     When the corner adjustment image Pv is displayed, the user, who can move the corner of the image formation region  12   e  (input image Pi) by operating the direction keys, operates the leftward key and the upward key as appropriate to move the selected upper left corner leftward and upward (step S 228 ). The upper left corner of the image formation region  12   e  is moved leftward by a predetermined amount whenever the leftward key is operated and upward by a predetermined amount whenever the upward key is operated (step S 229 ), as shown in  FIGS. 18A to 18I . Looking at the input image Pi projected on the projection surface S (see  FIG. 21C ), the user thus moves the upper left corner of the image formation region  12   e  leftward and upward by a necessary amount (see  FIG. 21D ). As a result, the image formation region  12   e  formed on the liquid crystal light valves  12  is so deformed that the upper left corner is moved leftward and upward as shown in  FIG. 22A . When the user then operates the enter key or the cancel key (step S 230 ), the control unit  20  completes moving the upper left corner and returns to the state in which the adjustment section selection image Pu is displayed (step S 221 ). 
     The user then operates the direction keys as required (step S 222 ) and now selects the identification image G 5  corresponding to the upper side (step S 223 ). When the user operates the enter key (step S 224 ), the control unit  20  displays the input image Pi with the side adjustment image Pw overlaid thereon (step S 227 ) and enlarges and displays the identification image G 5  in the enlarged image display section V of the side adjustment image Pw, as shown in  FIG. 21E . 
     When the side adjustment image Pw is displayed, the user operates the upward key as appropriate (step S 228 ) while looking at the input image Pi projected on the projection surface S (see  FIG. 21F ) to move the upper side of the image formation region  12   e  by a necessary amount. As a result, the image formation region  12   e  formed on the liquid crystal light valves  12  is so deformed that the upper side is moved upward as shown in  FIG. 22B . When the user operates the enter key or the cancel key (step S 230 ), the control unit  20  completes moving the upper side and returns to the state in which the adjustment section selection image Pu is displayed (step S 221 ). When the user then operates the cancel key (step S 225 ), the overlay display of the adjustment section selection image Pu is terminated (step S 226 ), and the input image Pi is displayed with the pincushion distortion eliminated. 
     The projector  2  can thus display the adjustment section selection image Pu, the corner adjustment image Pv, and the side adjustment image Pw in accordance with operation of the pincushion distortion correction key, the direction keys, the enter key, and the cancel key to correct pincushion distortion. 
     As described above, the projector  2  according to the present embodiment includes the light source apparatus  11 , the liquid crystal light valves  12  that modulate light outputted from the light source apparatus  11 , and the projection system including the projection lens  13  that projects image light modulated by the liquid crystal light valves  12 . The control unit  20  instructs the OSD processing unit  32  to display the eight identification images G 1  to G 8  corresponding to the four corners of a projected image Ao carried by the image light and the four sides between the corners by projecting the image light through the projection system. The input operation unit  42  receives operation of selecting one of the thus displayed eight identification images G 1  to G 8 , and the identification image G selected by the operation is so displayed that the selected identification image G is distinguishable from the other identification images G. In the state in which the selected identification image G is displayed, the input operation unit  42  receives operation of moving a corner or a predetermined point on a side. Based on the received operation, the image correction unit  33  moves the corner or the predetermined point on the side corresponding to the selected identification image G and corrects pincushion distortion based on the movement. Pincushion distortion can therefore be readily corrected by displaying the eight identification images G 1  to G 8  corresponding to the four corners and the four sides of a projected image Ao projected on the projection surface S, selecting one of the identification images G 1  to G 8  and displaying the selected identification image G, and correcting pincushion distortion based on operation on the identification image G. 
     Further, the control unit  20  adds the direction marks E movable by using the input operation unit  42  and corresponding to at least two axes to an identification image G selected by using the input operation unit  42  from the identification images G 1  to G 4  corresponding to the corners, whereas adding the direction mark E movable by using the input operation unit  42  and corresponding to one axis to an identification image G selected by using the input operation unit  42  from the identification images G 5  to G 8  corresponding to the sides. Since the optimum direction marks E are thus added to the corners and sides and displayed, the user can be guided to appropriate operation, whereby the operation of correcting pincushion distortion can be more readily carried out. 
     Further, the projector  2  can switch its operation mode between the pincushion distortion correction mode, in which pincushion distortion is corrected, and the trapezoidal distortion correction mode, in which trapezoidal distortion is corrected. In the trapezoidal distortion correction mode, the control unit  20  displays the four identification images C 1  to C 4  corresponding to the four corners of an image, and the input operation unit  42  receives operation of selecting one of the four identification images C 1  to C 4  displayed by the control unit  20 . In the state in which the control unit  20  displays the selected identification image C, the input operation unit  42  receives operation of moving the corner corresponding to the selected identification image C, and the image correction unit  33  moves the corner based on the operation received by the input operation unit  42  and corrects trapezoidal distortion based on the movement, whereby operation of correcting trapezoidal distortion can be readily carried out as well as operation of correcting pincushion distortion. 
     Further, since the control unit  20  disables display of the other seven identification images G that have not been selected by using the input operation unit  42  in the pincushion distortion correction mode, whereas disabling display of the other three identification images C that have not been selected by using the input operation unit  42  in the trapezoidal distortion correction mode, the operation of correcting pincushion distortion and trapezoidal distortion can be more readily carried out under optimum display. 
     In the state in which a corner or a predetermined point on a side selected by the input operation unit  42  is located at the limit of the movable range and hence unable to move in a predetermined direction, the control unit  20  reduces the visibility of the direction mark E corresponding to the predetermined direction, whereby the state of the displayed direction mark E notifies the user of the limit of the operation of moving the corner or the side, and the operation of correcting pincushion distortion can be more readily carried out. 
     The second embodiment is presented only by way of example of a specific aspect to which the invention is applied as the first embodiment is, and the invention can also be implemented in an aspect different from the embodiments described above. 
     For example, in the second embodiment, an identification image C selected in the corner selection image Ps is displayed in the corner adjustment image Pz and an identification image G corresponding to a corner or a side selected in the adjustment section selection image Pu is displayed in the corner adjustment image Pv or the side adjustment image Pw. That is, the other identification images C or G that have not been selected are not displayed. Alternatively, for example, part or the entire of the identification images C and G that have not been selected, as long as they are smaller than the identification images C and G that have been selected, may be displayed in the corner adjustment image Pz, the corner adjustment image Pv, and the side adjustment image Pw. Further, in the corner adjustment image Pz, the corner adjustment image Pv, and the side adjustment image Pw, the identification images C and G that have been selected are not necessarily enlarged, and the identification images C and G that have not been selected only need to be reduced in size or only do not need to be displayed. As described above, in the corner adjustment image Pz, the corner adjustment image Pv, and the side adjustment image Pw, the identification images C and G that have been selected only need to be enhanced by a greater amount before displayed than the identification images C and G that have not been selected. 
     Further, in the second embodiment, in the corner adjustment image Pz, the corner adjustment image Pv, and the side adjustment image Pw, the visibility of the color of the direction mark E pointing in a direction in which a corner or a side is unable to move is lowered, and when the direction key pointing in the unmovable direction is operated, the operation is ignored. Alternatively, when the direction key pointing in the unmovable direction is operated, a message notifying that a corner or a side is unable to move may be displayed, for example, in the message sections Mb and Md. 
     Further, in the second embodiment, the convenience of the user is improved if the user is readily notified of the position adjustment status. To this end, the user may be allowed to identify by looking at the adjustment section selection image Pu whether or not the adjustment of the position of a corner or a side has been completed. For example, when movement of a corner or a side (position adjustment) is completed, an adjustment completion mark representing that the position adjustment has been completed may be added to an identification image G in the adjustment section selection image Pu. Alternatively, the color of an identification image G having undergone position adjustment may be changed. 
     Further, in the second embodiment, when any of the direction keys is operated in the state in which the corner adjustment image Pv or the side adjustment image Pw is displayed, the color of the corresponding direction mark E may be temporarily changed in response to the operation. In this way, whenever a direction key is operated, the color of the corresponding direction mark E changes, whereby the user can recognize that operation of the direction key is normally received. 
     In the first embodiment, a description has been made of the projector  1  having a function of performing bow-shape correction (curved distortion correction), and in the second embodiment, a description has been made of the projector  2  that corrects trapezoidal distortion and distortion called pincushion distortion, barrel distortion, or otherwise named. A projector having all the functions described above can, of course, be provided. That is, a projector to which the invention is applied can be configured to perform the bow-shape correction, the trapezoidal distortion correction, and the pincushion distortion correction on an image projected on the projection surface S. 
     In the first and second embodiments, the description has been made with reference to the projector  2 , which is of three-panel type in which the three liquid crystal light valves  12 R,  12 G, and  12 B are used as light modulators, but the light modulators are not limited thereto. For example, the light modulators may alternatively have any of the following forms: a combination of a single-panel transmissive or reflective liquid crystal panel and a color wheel; a three-panel digital mirror device (DMD); and a combination of a single-panel digital mirror device (DMD) and a color wheel. When only a single liquid crystal panel or DMD is used as the display unit, a member corresponding to a cross-dichroic prism or any other combining system is not required. Further, each light modulator is not limited to a liquid crystal panel or a DMD, and any component capable of modulating light emitted from a light source can be used without any problem. Moreover, the light source apparatus  11 , which is formed of the discharge-type light source lamp  11   a , can alternatively be formed of an LED light source or any other solid-state light source or any other suitable light source. 
     Each functional unit of the projector  1  shown in  FIG. 1  and each functional unit of the projector  2  shown in  FIG. 7  represent functional configurations achieved by cooperation between hardware and software and are not limited to specific implementations. It is therefore not necessary to implement hardware corresponding to each functional unit, but a single processor that executes a program can, of course, serve as a plurality of functional units. Further, in the embodiments described above, part of the functions achieved by software may be achieved by hardware, or part of the functions achieved by hardware may be achieved by software. Additionally, the specific detailed configuration of each of the other units of the projector  2  can be arbitrarily changed to the extent that the change does not depart from the substance of the invention.