Patent Publication Number: US-9406280-B2

Title: Image display device, image display system, and method of controlling image display device

Description:
CROSS-REFERENCE 
     The entire disclosure of Japanese Patent Application No. 2013-055163, filed Mar. 18, 2013 and Japanese Patent Application No. 2013-055164, filed Mar. 18, 2013 is expressly incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to an image display device, an image display system, and a method of controlling an image display device. 
     2. Related Art 
     There is known a technology for transmitting an image from a terminal device such as a cellular phone to a projector using a wireless connection. In JP-A-2003-198870, it is described that a portable terminal transmits projection data to a projector wirelessly connected to the portable terminal. In JP-A-2009-98384, it is described that an image of a portable terminal is projected on a screen in an eye-friendly manner by using a server capable of the wireless connection in between. Further, there has been known an interactive projection system allowing the user to perform pseudo-writing on a projection surface on which an image is projected using a pen-type indicating body. 
     However, it is not achievable to perform drawing on the projection screen using a portable terminal in the system described above. 
     SUMMARY 
     An advantage of some aspects of the invention is to make an image to be output from an image display device to an electronic apparatus or displayed on the image display device, wherein in the image, a picture corresponding to a coordinate input from an electronic apparatus having a touch panel, or a coordinate input from an indicating body is drawn on an input image. 
     An aspect of the invention is directed to an image display device including a video signal acquisition section adapted to obtain a video signal representing a first image, a first coordinate data acquisition section adapted to obtain first coordinate data representing a coordinate of a point on the first image from an electronic apparatus having a touch panel, an image data acquisition section adapted to obtain image data representing a second image obtained by drawing a picture, which corresponds to the first coordinate data obtained by the first coordinate data acquisition section, on the first image, and an image data output section adapted to output the image data, which is obtained by the image data acquisition section, to the electronic apparatus. According to the image display device of the aspect of the invention, the second image obtained by drawing the picture, which corresponds to the coordinate input from the electronic apparatus, on the first image is output to the electronic apparatus. 
    
    
     
       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 diagram showing an overall configuration of a projection system. 
         FIG. 2  is a block diagram showing a functional configuration of the projection system. 
         FIG. 3  is a block diagram showing a hardware configuration of a projector. 
         FIG. 4  is a block diagram showing a hardware configuration of a PC. 
         FIG. 5  is a block diagram showing a hardware configuration of a tablet terminal. 
         FIG. 6  is a sequence chart showing a process in the projection system. 
         FIG. 7  is a flowchart showing a resizing process. 
         FIG. 8  is a diagram showing an overall configuration of a projection system. 
         FIG. 9  is a block diagram showing a functional configuration of the projection system. 
         FIG. 10  is a sequence chart showing a process in the projection system. 
         FIG. 11  is a diagram showing an overall configuration of a projection system. 
         FIG. 12  is a block diagram showing a functional configuration of the projection system. 
         FIG. 13  is a block diagram showing a hardware configuration of a projector. 
         FIG. 14  is a block diagram showing a hardware configuration of an indicating body. 
         FIG. 15  is a sequence chart showing a process in the projection system. 
         FIG. 16  is a diagram showing an overall configuration of a projection system. 
         FIG. 17  is a block diagram showing a functional configuration of the projection system. 
         FIG. 18  is a sequence chart showing a process in the projection system. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     First Embodiment 
       FIG. 1  is a diagram showing an overall configuration of a projection system PS1 according to a first embodiment of the invention. The projection system PS1 has a projector  1 , a personal computer  2 , a tablet terminal  3 , a controller RC, and a screen SC. The projector  1  is a device for projecting an image (hereinafter referred to as an “input image”) represented by a video signal on the screen SC. The projector  1  is an example of an image display device. The personal computer (hereinafter referred to as a “PC”)  2  outputs the video signal to the projector  1 . The PC  2  is connected to the projector  1  with an image signal cable and a USB (Universal Serial Bus) cable with wired connection. The PC  2  is an example of an external device as a video signal source. The tablet terminal  3  functions as a pointing device (an input device) for operating the PC  2 . The tablet terminal  3  is connected to the projector  1  via a wireless LAN (Local Area Network) compliant with, for example, Wi-Fi (Wireless Fidelity; a registered trademark). The tablet terminal  3  is an example of an electronic apparatus. By the user operating a touch panel  34  of the tablet terminal  3 , the input operation to the PC  2  is performed. Specifically, when the user operates the touch panel  34 , a picture corresponding to the operation is drawn on the input image in the PC  2 . The controller RC is a device for controlling the projector  1  using wireless communication such as infrared communication, a so-called remote controller. The screen SC is a plane reflecting an image (hereinafter referred to as a “projection image”) projected from the projector  1 . 
       FIG. 2  is a block diagram showing a functional configuration of the projection system PS1. The projector  1  includes a video signal acquisition section  101 , an image adjustment section  102 , an image processing section  103 , a projection section  104 , a coordinate data acquisition section  105 , a coordinate conversion section  106 , a coordinate data output section  107 , an image data acquisition section  108 , an image compression section  109 , and an image data output section  110 . The video signal acquisition section  101  obtains the video signal output from the PC  2 . The image adjustment section  102  changes (resizes) the size (the resolution) of the input image to a size corresponding to the projection section  104 . Hereinafter, a process of changing the size of the input image is expressed as a “resizing process.” The image processing section  103  performs predetermined image processing on the input image (hereinafter referred to as a “resized image”) having been resized. The projection section  104  projects the input image, on which the image processing has been performed by the image processing section  103 , on the screen SC as a projection image. The coordinate data acquisition section  105  (an example of a first coordinate data acquisition section) obtains the coordinate data (an example of first coordinate data) representing the coordinate of a point on the input image from the tablet terminal  3 . The coordinate conversion section  106  converts a coordinate system of the coordinate represented by the coordinate data obtained by the coordinate data acquisition section  105  into a coordinate system of the input image. The coordinate data output section  107  outputs the coordinate data, the coordinate system of which has been converted by the coordinate conversion section  106 , to the PC  2 . The image data acquisition section  108  obtains the image data representing the resized image from the image adjustment section  102 . Hereinafter, for the sake of convenience of explanation, the input image, in which the picture corresponding to the coordinate data has not been drawn, is referred to as a “primary image,” and an image obtained by drawing the picture corresponding to the coordinate data on the primary image is referred to as a “secondary image.” The image data obtained by the image data acquisition section  108  represents the resized image of the primary image or the secondary image. The image compression section  109  compresses the image data obtained by the image data acquisition section  108 . The image data output section  110  outputs the image data compressed by the image compression section  109  to the tablet terminal  3 . 
     The PC  2  includes a video signal output section  201 , a coordinate data acquisition section  202 , and a drawing section  203 . The video signal output section  201  outputs the video signal to the projector  1 . The coordinate data acquisition section  202  obtains the coordinate data output by the projector  1 . The drawing section  203  draws the picture, which corresponds to the coordinate data obtained by the coordinate data acquisition section  202 , on the primary image to thereby generate the secondary image. 
     The tablet terminal  3  includes a coordinate conversion section  301 , a coordinate data output section  302 , an image data acquisition section  303 , and a display control section  304 . The coordinate conversion section  301  converts the coordinate of a point designated by the user on the touch panel  34  into the coordinate of a point on the primary image, and then generates the coordinate data representing the coordinate. The coordinate data output section  302  outputs the coordinate data generated by the coordinate conversion section  301  to the projector  1 . The image data acquisition section  303  obtains the image data output by the projector  1 . The display control section  304  displays the image, which is represented by the image data thus obtained by the image data acquisition section  303 , on the touch panel  34 . It should be noted that the touch panel  34  has a display section formed of a liquid crystal panel or the like. 
       FIG. 3  is a block diagram showing a hardware configuration of the projector  1 . The projector  1  includes a central processing unit (CPU)  10 , a read only memory (ROM)  11 , a random access memory (RAM)  12 , an interface (IF) section  13 , an image processing circuit  14 , a projection unit  15 , a light receiving section  16 , an operation panel  17 , and an input processing section  18 . The CPU  10  is a control device which executes a control program  11 A to thereby control the sections of the projector  1 . The ROM  11  is a nonvolatile storage device storing a variety of programs and data. The ROM  11  stores the control program  11 A to be executed by the CPU  10 . The RAM  12  is a volatile storage device for storing data. The RAM  12  includes a frame memory  12   a  and a frame memory  12   b . The frame memory  12   a  is an area for storing one frame of the resized image. The frame memory  12   b  is an area for storing one frame of the projection image. 
     The IF section  13  communicates with an information processing device such as the PC  2  and the tablet terminal  3 . The IF section  13  is provided with a variety of types of terminals (e.g., a VGA terminal, a USB terminal, a wired or wireless LAN interface, an S terminal, an RCA terminal, and an HDMI (High-Definition Multimedia Interface; a registered trademark) terminal) for connecting to the information processing device. In the present embodiment, the IF section  13  communicates with the PC  2  via the VGA terminal and the USE terminal. Specifically, the IF section  13  obtains the video signal from the PC  2  via the VGA terminal, and outputs the coordinate data to the PC  2  via the USB terminal. The IF section  13  extracts vertical and horizontal sync signals from the video signal obtained from the PC  2 . The IF section  13  also communicates with the tablet terminal  3  via the wireless LAN interface. The image processing circuit  14  performs a resizing process and predetermined image processing on the input image. The image processing circuit  14  writes the resized image in the frame memory  12   a , and writes the resized image (i.e., the projection image) after the image processing in the frame memory  12   b.    
     The projection unit  15  includes a light source  151 , liquid crystal panels  152 , an optical system  153 , a light source drive circuit  154 , a panel drive circuit  155 , and an optical system drive circuit  156 . The light source  151  has a lamp such as a high-pressure mercury lamp, a halogen lamp, or a metal halide lamp, or a light emitting body such as a light emitting diode (LED) or a laser diode, and irradiates the liquid crystal panels  152  with light. The liquid crystal panels  152  are each a light modulation device for modulating the light emitted from the light source  151  in accordance with the image data. In the present example, each of the liquid crystal panels  152  has a plurality of pixels arranged in a matrix. Each of the liquid crystal panels  152  has the resolution of, for example, XGA (eXtended Graphics Array), and has a display area composed of 1024×768 pixels. In this example, the liquid crystal panels  152  are each a transmissive liquid crystal panel, and the transmittance of each of the pixels is controlled in accordance with the image data. The projector  1  has three liquid crystal panels  152  corresponding respectively to the three primary colors of RGB. The light from the light source  151  is separated into colored lights of three colors of RGB, and the colored lights respectively enter the corresponding liquid crystal panels  152 . The colored lights, which have been modulated while passing through the respective liquid crystal panels, are combined by a cross dichroic prism or the like, and the combined light is then emitted to the optical system  153 . The optical system  153  includes a lens for enlarging the light modulated by the liquid crystal panels  152  into the image light and then projecting the light on the screen SC, a zoom lens for performing expansion/contraction of the image to be projected, and the focus adjustment, a zoom controlling motor for controlling a zoom level, a focus adjusting motor for performing the focus adjustment, and so on. The light source drive circuit  154  drives the light source  151  with the control by the CPU  10 . The panel drive circuit  155  drives the liquid crystal panel  152  in accordance with the image data output from the CPU  10 . The optical system drive circuit  156  drives the motors included in the optical system  153  with the control by the CPU  10 . 
     The light receiving section  16  receives an infrared signal transmitted from the controller RC, decodes the infrared signal thus received, and then outputs the result to the input processing section  18 . The operation panel  17  has buttons and switches for performing ON/OFF of the power and a variety of operations of the projector  1 . The input processing section  18  generates the information representing the operation content by the controller RC or the operation panel  17 , and then outputs the information to the CPU  10 . 
     In the projector  1 , the CPU  10  executing the program is an example of the coordinate conversion section  106 , the image data acquisition section  108 , and the image compression section  109 . The IF section  13 , which is controlled by the CPU  10  executing the program, is an example of the video signal acquisition section  101 , the coordinate data acquisition section  105 , the coordinate data output section  107 , and the image data output section  110 . In the projector  1 , the image processing circuit  14 , which is controlled by the CPU  10  executing the program, is an example of the image adjustment section  102  and the image processing section  103 . The projection unit  15 , which is controlled by the CPU  10  executing the program, is an example of the projection section  104 . 
       FIG. 4  is a block diagram showing a hardware configuration of the PC  2 . The PC  2  includes a CPU  20 , a ROM  21 , a RAM  22 , an IF section  23 , a display section  24 , and an input section  25 . The CPU  20  is a control device which executes a program to thereby control the sections of the PC  2 . The ROM  21  is a nonvolatile storage device storing a variety of programs and data. The RAM  22  is a volatile storage device for storing data. The IF section  23  communicates with an information processing device such as the projector  1 . The IF section  23  is provided with a variety of types of terminals for connecting to the information processing device. The display section  24  includes a display device such as a liquid crystal display or an organic electroluminescence (EL) display. The input section  25  is a device for receiving the input by the user, and is provided with a keyboard, a mouse, a variety of types of buttons, and so on. In the PC  2 , the CPU  20  executing the program is an example of the drawing section  203 . The IF section  23 , which is controlled by the CPU  20  executing the program, is an example of the video signal output section  201  and the coordinate data acquisition section  202 . 
       FIG. 5  is a block diagram showing a hardware configuration of the tablet terminal  3 . The tablet terminal  3  includes a CPU  30 , a ROM  31 , a RAM  32 , an IF section  33 , and the touch panel  34 . The CPU  30  is a control device which executes a program to thereby control the sections of the tablet terminal  3 . The ROM  31  is a nonvolatile storage device storing a variety of programs and data. The RAM  32  is a volatile storage device for storing data. The IF section  33  communicates with an information processing device such as the projector  1 . The IF section  33  is provided with a wireless LAN interface for connecting to the projector  1 . The touch panel  34  is an input device having a panel for sensing a coordinate stacked on a display surface of, for example, a liquid crystal display. A touch panel of, for example, an optical type, a resistance film type, a capacitance type, or an ultrasonic type is used for the touch panel  34 . In the tablet terminal  3 , the CPU  30  executing the program is an example of the coordinate conversion section  301 , and the display control section  304 . The IF section  33 , which is controlled by the CPU  30  executing the program, is an example of the coordinate data output section  302  and the image data acquisition section  303 . 
       FIG. 6  is a sequence chart showing a process executed in the projection system PS1. In this example, the PC  2  executes a drawing program for drawing a picture on the input image (here, the image displayed on the display section  24 ). In such a circumstance, in the case of attempting to perform drawing on the input image (and the projection image), there can be cited a method of operating the input section  25  (e.g., the mouse) of the PC  2 . However, since the projector  1  and the PC  2  are connected to each other with the wired connection, there arises a distance limitation in performing the drawing in a place distant from the projector  1 . The projection system PS1 makes the tablet terminal  3  function as a pointing device for operating the PC  2  to thereby suppress the distance limitation in performing the drawing. The process shown in  FIG. 6  is triggered by, for example, the fact that the PC  2  outputs the video signal (here, the video signal representing the primary image) to the projector  1 . 
     In the step SA 1 , the CPU  10  of the projector  1  obtains the video signal from the PC  2 . In the step SA 2 , the CPU  10  performs the resizing process on the input image. Due to the resizing process, the CPU  10  changes the size of the input image to a size corresponding to the liquid crystal panels  152 . 
       FIG. 7  is a flowchart showing a specific processing content of the resizing process. Hereinafter, the case (the case of contracting the input image) in which the size of the input image is larger than the size of each of the liquid crystal panels  152  will be explained as an example. In the step SA 21 , the CPU  10  obtains the size of the input image. The size of the image mentioned here denotes the number of pixels of the image in the vertical direction and the number of the pixels of the image in the horizontal direction. The video signal includes a signal representing the size of the input image, and the CPU  10  obtains the size of the input image based on the signal. The CPU  10  stores the size of the input image thus obtained in the RAM  12 . In the step SA 22 , the CPU  10  obtains the size of each of the liquid crystal panels  152 . Specifically, the CPU  10  reads out the information representing the resolution of each of the liquid crystal panels  152  stored in the ROM  11  to obtain the size of each of the liquid crystal panels  152 . 
     In the step SA 23 , the CPU  10  determines whether or not the aspect ratio of the input image and the aspect ratio of each of the liquid crystal panels  152  are equal to each other. Specifically, the CPU  10  calculates the aspect ratio of the input image and the aspect ratio of each of the liquid crystal panels  152  based on the size of the input image and the size of each of the liquid crystal panels  152 , respectively, and then compares these aspect ratios. In the case in which it is determined that the aspect ratio of the input image and the aspect ratio of each of the liquid crystal panels  152  are not equal to each other (NO in the step SA 23 ), the CPU  10  makes a transition of the process to the step SA 24 . In the case in which it is determined that the aspect ratio of the input image and the aspect ratio of each of the liquid crystal panels  152  are equal to each other (YES in the step SA 23 ), the CPU  10  makes a transition of the process to the step SA 25 . For example, in the case in which the size of the input image is 800 by 1280, the aspect ratio is 16:10. Further, in the case in which the size of each of the liquid crystal panels  152  is 768 by 1024, the aspect ratio is 4:3. Therefore, in this case, it is determined that the aspect ratio of the input image and the aspect ratio of each of the liquid crystal panels  152  are not equal to each other. 
     In the step SA 24 , the CPU  10  calculates an offset value α. The offset value denotes a value representing the horizontal number of the pixels to be uniformly removed from the input image in the resizing process. The CPU  10  reads out the size of the input image and the size of each of the liquid crystal panels  152  from the RAM  12  to calculate the offset value α using, for example, Formula (1) below.
 
α= L 1−( L 2 ×L 3 /L 4)  (1)
 
(L1: the horizontal pixel number of the input image, L2: the vertical pixel number of the input image, L3: the horizontal pixel number of each of the liquid crystal panels  152 , L4: the vertical pixel number of each of the liquid crystal panels  152 )
 
     The CPU  10  stores the offset value α thus calculated in the RAM  12 . In the example described above, the pixel numbers are L1=1280, L2=800, L3-1024, and L4=768, and the offset value α becomes α=214. 
     In the step SA 25 , the CPU  10  determines whether or not the size of the input image (hereinafter referred to as an “offset input image size”) defined taking the offset value α into consideration and the size of each of the liquid crystal panels  152  are equal to each other. Specifically, the CPU  10  reads out the size of the input image and the offset value α separately from the RAM  12 , and then subtracts the offset value α from the horizontal pixel number of the input image to thereby calculate the offset input image size. Then, the CPU  10  reads out the size of each of the liquid crystal panels  152  from the ROM  11 , and then compares the offset input image size and the size of each of the liquid crystal panels  152  with each other. In the case in which it is determined that the offset input image size and the size of each of the liquid crystal panels  152  are not equal to each other (NO in the step SA 25 ), the CPU  10  makes a transition of the process to the step SA 26 . In the case in which it is determined that the offset input image size and the size of each of the liquid crystal panels  152  are equal to each other (YES in the step SA 25 ), the CPU  10  makes a transition of the process to the step SA 27 . In the example of the sizes described above, the offset input image size is 800 by 1066, and the size of the projection image is 768 by 1024. Therefore, it is determined that the offset input image size and the size of each of the liquid crystal panels  152  are not equal to each other. 
     In the step SA 26 , the CPU  10  calculates a conversion coefficient β. The conversion coefficient denotes a value representing a ratio between the size of the input image and the size of each of the liquid crystal panels  152 . The CPU  10  reads out the size of the input image and the size of the projection image from the RAM  12  to calculate the conversion coefficient β using, for example, Formula (2) below.
 
β= L 4 /L 2  (2)
 
     The CPU  10  stores the conversion coefficient β thus calculated in the RAM  12 . In the example described above, the numbers are L2=800, L4=768, and the conversion coefficient β becomes β=0.96. It should be noted that the conversion coefficient β can also be calculated with Formula (3) below using the offset value α.
 
β= L 3/( L 1−α)  (3)
 
     In the step SA 27 , the CPU  10  resizes the input image using the offset value α and the conversion coefficient β. Specifically, the CPU  10  converts the coordinate (x, y) of each of the pixels in the input image into the coordinate (X, Y) using Formula (4) below. It should be noted that “x” and “X” each represent a coordinate in the horizontal direction of the image, and “y” and “Y” each represent a vertical coordinate of the image. 
     
       
         
           
             
               
                 
                   
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     The CPU  10  writes the image data representing the resized image in the frame memory  12   a.    
       FIG. 6  is referred to again. In the step SA 3 , the CPU  10  compresses the image data representing the resized image. Specifically, the CPU  10  reads out the image data from the frame memory  12   a  to thereby obtain the image data, and then compresses the image data so as to correspond to the frequency band of the wireless LAN. The CPU  10  compresses the image data using, for example, the JPEG (Joint Photographic Experts Group) method. The compression of the image data is performed, for example, every several frames, or every predetermined period of time. The CPU  10  stores the compressed image data in the RAM  12 . In the step SA 4 , the CPU  10  reads out the compressed image data from the RAM  12 , and then outputs the image data to the tablet terminal  3 . 
     In the step SA 5 , the CPU  10  performs the image processing on the resized image. Specifically, the CPU  10  reads out the image data from the frame memory  12   a , and then performs predetermined image processing (e.g., a process of superimposing an OSD (On Screen Display) image, a keystone distortion correction process, a frame rate conversion process, and an overdrive process) on the resized image. The CPU  10  writes the image data representing the resized image, on which the image processing has been performed, in the frame memory  12   b . In the step SA 6 , the CPU  10  drives the liquid crystal panels  152  in accordance with the image data stored in the frame memory  12   b . Specifically, the CPU  10  reads out the image data from the frame memory  12   b , and then outputs the image data to the panel drive circuit  155 . 
     In the step SA 7 , the CPU  30  of the tablet terminal  3  displays the image, which corresponds to the resized image represented by the image data obtained from the projector  1 , on the touch panel  34 . Specifically, the CPU  30  changes the size of the resized image represented by the image data to a size corresponding to the touch panel  34 , and then displays the resized image, which has been changed in size, on the touch panel  34 . Due to the process in the step SA 7 , the image corresponding to the projection image is displayed on the touch panel  34 . In the step SA 8 , the CPU  30  converts the physical coordinate of the point designated by the user on the touch panel  34  into the coordinate of a point on the resized image represented by the image data. The process in the step SA 8  is triggered by the fact that the touch panel  34  detects the operation by the user. The conversion between the physical coordinate on the touch panel  34  and the coordinate of the point on the resized image is performed using a predetermined formula. The CPU  30  stores the coordinate data representing the coordinate of the point on the resized image in the RAM  32 . In the step SA 9 , the CPU  30  reads out the coordinate data from the RAM  32  and then outputs the coordinate data to the projector  1 . It should be noted that the processes in the steps SA 8  and SA 9  are performed every time the touch panel  34  detects the operation by the user, and the plurality of coordinate data is sequentially output to the projector  1 . 
     In the step SA 10 , the CPU  10  of the projector  1  performs a coordinate conversion process. The coordinate conversion process denotes a process of converting the coordinate system of the coordinate represented by the coordinate data into the coordinate system of the input image. Due to the coordinate conversion process, the CPU  10  converts the coordinate system of the coordinate of the resized image represented by the coordinate data obtained from the tablet terminal  3  into the coordinate system of the (original) input image on which the resizing process has not been yet performed. Specifically, the CPU  10  converts the coordinate (Xi, Yi) represented by the coordinate data obtained from the tablet terminal  3  into the coordinate (xi, yi) in the original input image with Formula (5) below using the offset value α and the conversion coefficient β read out from the RAM  12 . 
     
       
         
           
             
               
                 
                   
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     The CPU  10  stores the converted coordinate (xi, yi) in the RAM  12 . For example, in the example of the size described above, in the case in which the coordinate (Xi, Yi) represented by the coordinate data obtained from the tablet terminal  3  is (275, 480), the coordinate (xi, yi) in the original input image becomes (500, 500). In the step SA 11 , the CPU  10  reads out the coordinate (xi, yi) from the RAM  12  and then outputs the coordinate data representing the coordinate to the PC  2 . 
     In the step SA 12 , the CPU  20  of the PC  2  draws a picture corresponding to the coordinate data obtained from the projector  1  on the input image (the primary image). Specifically, the CPU  20  interpolates the coordinates represented by the plurality of coordinate data to thereby draw the picture (hereinafter a “trajectory image”) corresponding to a trajectory of the point designated by the user on the touch panel  34 . The CPU  20  stores the sequence, in which the coordinates sequentially output from the projector  1  are obtained, in the RAM  12 , and forms the image by connecting the plurality of coordinates to each other along the sequence while interpolating the coordinates as the trajectory image. The sequence in which the coordinates are obtained is stored in the RAM  22  together with the coordinates when the CPU  20  obtains the coordinate data from the projector  1 . Then, the CPU  20  combines the trajectory image and the primary image with each other to generate the secondary image. The CPU  20  stores the image data representing the secondary image in the RAM  22 . In the step SA 13 , the CPU  20  reads out the image data representing the secondary image from the RAM  22 , and then outputs a video signal representing the image data to the projector  1 . 
     In the steps SA 14  through SA 18 , the CPU  10  of the projector  1  performs substantially the same processes as the processes in the steps SA 2  through SA 6  on the secondary image. Due to the process in the step SA 18 , the projection image based on the secondary image is projected on the screen SC. In the step SA 19 , the CPU  30  of the tablet terminal  3  displays the image, which corresponds to the resized image of the secondary image, on the touch panel  34  using substantially the same process as the process in the step SA 7 . Due to the processes described hereinabove, the picture corresponding to the operation on the touch panel  34  is drawn on the input image (and the projection image), and thus, it is possible to make the tablet terminal  3  function as a pointing device for operating the PC  2 . Therefore, the drawing can be performed even in the place distant from the PC  2  and the projector  1  (and the screen SC), and thus, the distance limitation in performing the drawing can be suppressed. Further, the drawing can more intuitively be performed compared to the case of operating the input section  25  of the PC  2 . As an application example of the projection system PS1, it is possible that a teacher makes a student operate the tablet terminal  3  in a classroom of a school to thereby perform drawing on the input image in a place distant from the PC  2 . 
     Second Embodiment 
       FIG. 8  is a diagram showing an overall configuration of a projection system PS2 according to a second embodiment of the invention. Hereinafter, the projection system PS2 will be explained focusing on the different parts from the projection system PS1. In the projection system PS2, AV equipment such as a DVD player is used instead of the PC  2  described above. The DVD player  4  outputs the video signal to the projector  1 . The DVD player  4  is connected to the HDMI terminal of the projector  1  with a cable using wired connection. In the projection system PS2, the projector  1  executes a drawing program for drawing a picture on the input image. In the case in which the projector  1  is executing the drawing program, the tablet terminal  3  functions as the pointing device for operating the projector  1 . When the user operates the touch panel  34 , a picture corresponding to the operation is drawn on the input image in the projector  1 . 
       FIG. 9  is a block diagram showing a functional configuration of the projection system PS2. The projector  1  has a drawing section  111  and an image data combining section  112  instead of the coordinate conversion section  106  and the coordinate data output section  107  shown in  FIG. 2 . The drawing section  111  draws the picture corresponding to the coordinate data obtained by the coordinate data acquisition section  105 . The image data combining section  112  combines the picture drawn by the drawing section  111  and the resized image of the primary image with each other to generate image data representing the secondary image. The image processing section  103  performs predetermined image processing on the secondary image represented by the image data generated by the image data combining section  112 . The image data acquisition section  108  obtains the image data generated by the image data combining section  112 . In the projector  1  according to the second embodiment, the CPU  10  executing the program is an example of the image data acquisition section  108 , the image compression section  109 , the drawing section  111 , and the image data combining section  112 . 
       FIG. 10  is a sequence chart showing a process executed in the projection system PS2. The following process is triggered by the fact that an instruction for making the projector  1  execute the drawing program is input to the projector  1  in a state in which the DVD player  4  is outputting the video signal (here, the video signal representing the primary image) to the projector  1 . The instruction for executing the drawing program is input in response to the user operating the controller RC. 
     In the step SB 1 , the CPU  10  of the projector  1  obtains the video signal from the DVD player  4 . In the steps SB 2  through SB 9 , the CPU  10 , and the CPU  30  of the tablet terminal  3  perform substantially the same processes as the processes in the steps SA 2  through SA 9 . 
     In the step SB 10 , the CPU  10  draws the picture corresponding to the coordinate data obtained from the tablet terminal  3 . Specifically, the CPU  10  interpolates the coordinates (Xi, Yi) represented by the plurality of coordinate data to thereby draw the trajectory image. The CPU  10  stores the trajectory image in the RAM  12 . In the step SB 11 , the CPU  10  combines the trajectory image and the resized image of the primary image with each other to generate the secondary image. Specifically, the CPU  10  respectively reads out the resized image of the primary image from the frame memory  12   a , and the trajectory image from the RAM  12 , to combine the trajectory image on the resized image. The CPU  10  writes the image data representing the secondary image thus generated in the frame memory  12   a.    
     In the steps SB 12  through SB 16 , the CPU  10  and the CPU  30  perform substantially the same processes as the processes in the steps SB 3  through SB 7  on the secondary image. Due to the processes described hereinabove, the picture corresponding to the operation on the touch panel  34  is drawn on the input image (and the projection image), and thus, it is possible to make the tablet terminal  3  function as a pointing device for operating the projector  1 . Therefore, the drawing can be performed even in the place distant from the projector  1  (and the screen SC), and thus, the distance limitation in performing the drawing can be suppressed. 
     Third Embodiment 
       FIG. 11  is a diagram showing an overall configuration of a projection system PS3 according to a third embodiment of the invention. The projection system PS3 includes a projector  5 , a personal computer  2 , a pointing body  6 , a tablet terminal  3 , a controller RC, and a screen SC. The projector  5  is a device for projecting an image (hereinafter referred to as an “input image”) represented by a video signal on the screen SC. The projector  5  is a front projection short focus projector, and is disposed at a position relatively close to the screen SC. In the example shown in  FIG. 11 , the projector  5  is disposed above the screen SC. The personal computer (hereinafter referred to as a “PC”)  2  outputs the video signal to the projector  5 . The PC  2  is connected to the projector  5  with an image signal cable and a USB cable with wired connection. The PC  2  is an example of an external device to be an input source of the video signal to the projector  5 . The pointing body  6  is a pen-shaped or rod-shaped operation device used as a writing material when the user electronically writes a handwritten character or image in the image (hereinafter referred to as a “projection image”) projected from the projector  5 . The projector  5  is provided with a function of continuously identifying the position of the pointing body  6  on the screen SC. The tablet terminal  3  is an electronic apparatus used when the user electronically writes the handwritten character or image on the input image at a position distant from the screen SC. When the user operates the touch panel  34  of the tablet terminal  3 , a picture corresponding to the operation is drawn on the input image in the PC  2 . The tablet terminal  3  is connected to the projector  5  via a wireless LAN compliant with, for example, Wi-Fi. The controller RC is a device for controlling the projector  5  using wireless communication such as infrared communication, a so-called remote controller. The screen SC is a plane for reflecting the projection image. 
       FIG. 12  is a block diagram showing a functional configuration of the projection system PS3. The pointing body  6  includes a pressure detection section  601  and a light emitting section  602 . The pressure detection section  601  detects the fact that the tip of the pointing body  6  is pressed against the screen SC due to the writing action by the user. The light emitting section  602  outputs light when the pressure detection section  601  detects the fact that the tip of the pointing body  6  is pressed against the screen SC. 
     The projector  5  includes a video signal acquisition section  501 , an image adjustment section  502 , an image processing section  503 , a projection section  504 , an imaging section  505 , a coordinate data generation section  506 , a coordinate conversion section  507 , a coordinate data acquisition section  508 , a coordinate conversion section  509 , an integration section  510 , a coordinate data output section  511 , an image data acquisition section  512 , an image compression section  513 , and an image data output section  514 . The video signal acquisition section  501  obtains the video signal output from the PC  2 . The image adjustment section  502  changes (resizes) the size (the resolution) of the input image to a size corresponding to the projection section  504 . The image processing section  503  performs predetermined image processing on the resized input image. The image processing section  503  outputs the resized image on which the image processing has been performed to the projection section  504 . The image processing section  503  is an example of an output section for outputting the video signal to the projection section  504 . The projection section  504  projects the resized image, on which the image processing has been performed, on the screen SC as the projection image. 
     The imaging section  505  takes an image of the screen SC to generate the image data representing the light output from the projection image and the pointing body  6 . The coordinate data generation section  506  (an example of a second coordinate data acquisition section) generates the coordinate data (hereinafter referred to as “pen input data”) representing the coordinate of the point indicated by the user on the projection image with the pointing body  6  based on the image data generated by the imaging section  505 . The pen input data is an example of second coordinate data in the invention. The coordinate conversion section  507  converts a coordinate system of the coordinate represented by the pen input data generated by the coordinate data generation section  506  into a coordinate system of the input image. 
     The coordinate data acquisition section  508  (an example of the first coordinate data acquisition section) obtains the coordinate data (hereinafter referred to as “touch input data”), which represents the coordinate of a point on the resized image, from the tablet terminal  3 . The touch input data is an example of first coordinate data in the invention. The coordinate conversion section  509  converts a coordinate system of the coordinate represented by the touch input data obtained by the coordinate data acquisition section  508  into a coordinate system of the input image. The integration section  510  generates coordinate data (hereinafter referred to as “integrated coordinate data”) obtained by integrating the pen input data generated by the coordinate data generation section  506  and the touch input data obtained by the coordinate data acquisition section  508  with each other. The “integration” denotes a process of converting the coordinates input from a plurality of pointing devices (the pointing body  6  and the tablet terminal  3  in this example) into those having a format, which can be decoded by an element (the drawing section  203  in this example) using these coordinates. In other words, in this example, the integration of the coordinate data is performed for reflecting the coordinate represented by the pen input data and the coordinate represented by the touch input data in the same coordinate data. The integrated coordinate data is an example of third coordinate data in the invention. The coordinate data output section  511  outputs the integrated coordinate data generated by the integration section  510  to the PC  2 . 
     The image data acquisition section  512  obtains the image data representing the resized image from the image adjustment section  502 . Hereinafter, for the same of convenience of explanation, the input image, in which the picture corresponding to the integrated coordinate data has not been drawn, is referred to as a “primary image,” and an image obtained by drawing the picture corresponding to the integrated coordinate data on the primary image is referred to as a “secondary image.” The image data obtained by the image data acquisition section  512  represents the resized image of the primary image or the secondary image. The image compression section  513  compresses the image data obtained by the image data acquisition section  512 . The image data output section  514  outputs the image data compressed by the image compression section  513  to the tablet terminal  3 . 
     The PC  2  includes a video signal output section  201 , a coordinate data acquisition section  202 , and a drawing section  203 . The video signal output section  201  outputs the video signal to the projector  5 . The coordinate data acquisition section  202  obtains the integrated coordinate data output by the projector  5 . The drawing section  203  draws the picture corresponding to the integrated coordinate data obtained by the coordinate data acquisition section  202  on the primary image to thereby generate the secondary image. 
     The tablet terminal  3  includes a coordinate conversion section  301 , a coordinate data output section  302 , an image data acquisition section  303 , and a display control section  304 . The coordinate conversion section  301  converts the coordinate of a point pointed by the user on the touch panel  34  into the coordinate of a point on the resized image to generate the touch input data representing the coordinate. The coordinate data output section  302  outputs the touch input data generated by the coordinate conversion section  301  to the projector  5 . The image data acquisition section  303  obtains the image data output by the projector  5 . The display control section  304  displays the image, which corresponds to the resized image, and is represented by the image data thus obtained by the image data acquisition section  303 , on the touch panel  34 . 
       FIG. 13  is a block diagram showing a hardware configuration of the projector  5 . The projector  5  includes a CPU  50 , a ROM  51 , a RAM  52 , an interface (IF) section  53 , an image processing circuit  54 , a projection unit  55 , image sensors  56 , a light receiving section  57 , an operation panel  58 , and an input processing section  59 . The CPU  50  is a control device which executes a control program  51 A to thereby control the sections of the projector  5 . The ROM  51  is a nonvolatile storage device storing a variety of programs and data. The ROM  51  stores the control program  51 A to be executed by the CPU  50 . The RAM  52  is a volatile storage device for storing data. The RAM  52  includes a frame memory  52   a  and a frame memory  52   b . The frame memory  52   a  is an area for storing one frame of the resized image. The frame memory  52   b  is an area for storing one frame of the projection image. 
     The IF section  53  communicates with an external device such as the PC  2  and the tablet terminal  3 . The IF section  53  is provided with a variety of types of terminals (e.g., a VGA terminal, an USB terminal, a wired or wireless LAN interface, an S terminal, an RCA terminal, and an HDMI terminal) for connecting to the external device. In the present embodiment, the IF section  53  communicates with the PC  2  via the VGA terminal and the USE terminal. Specifically, the IF section  53  obtains the video signal from the PC  2  via the VGA terminal, and outputs the integrated coordinate data to the PC  2  via the USB terminal. The IF section  53  extracts vertical and horizontal sync signals from the video signal obtained from the PC  2 . The IF section  53  also communicates with the tablet terminal  3  via the wireless LAN interface. The image processing circuit  54  performs a resizing process and predetermined image processing on the input image. The image processing circuit  54  writes the resized image in the frame memory  52   a , and writes the resized image (i.e., the projection image) after the image processing in the frame memory  52   b.    
     The projection unit  55  includes a light source  551 , liquid crystal panels  552 , an optical system  553 , a light source drive circuit  554 , a panel drive circuit  555 , and an optical system drive circuit  556 . The light source  551  has a lamp such as a high-pressure mercury lamp, a halogen lamp, or a metal halide lamp, or a light emitting body such as an LED or a laser diode, and irradiates the liquid crystal panels  552  with light. The liquid crystal panels  552  are each a light modulation device for modulating the light emitted from the light source  551  in accordance with the image data. In the present example, each of the liquid crystal panels  552  has a plurality of pixels arranged in a matrix. Each of the liquid crystal panels  552  has the resolution of, for example, XGA, and has a display area composed of 1024×768 pixels. In this example, the liquid crystal panels  552  are each a transmissive liquid crystal panel, and the transmittance of each of the pixels is controlled in accordance with the image data. The projector  5  has three liquid crystal panels  552  corresponding respectively to the three primary colors of RGB. The light from the light source  551  is separated into colored lights of three colors of RGB, and the colored lights respectively enter the corresponding liquid crystal panels  552 . The colored lights, which have been modulated while passing through the respective liquid crystal panels, are combined by a cross dichroic prism or the like, and the combined light is then emitted to the optical system  553 . The optical system  553  includes a lens for enlarging the light modulated by the liquid crystal panels  552  into the image light and then projecting the light on the screen SC, a zoom lens for performing expansion/contraction of the image to be projected, and the focus adjustment, a zoom controlling motor for controlling a zoom level, a focus adjusting motor for performing the focus adjustment, and so on. The light source drive circuit  554  drives the light source  551  with the control by the CPU  50 . The panel drive circuit  555  drives the liquid crystal panels  552  in accordance with the image data output from the CPU  50 . The optical system drive circuit  556  drives the motors included in the optical system  553  with the control by the CPU  50 . 
     The image sensors  56  are a solid-state imaging element group for taking the image of the screen SC to generate the image data. The image sensors  56  are each formed of, for example, a CMOS image sensor or a COD image sensor. The projector  5  has a plurality of image sensors  56  (the image sensor group), and these image sensors  56  take the image of the screen SC with a field angle including the largest range in which the projection unit  15  can project the projection image. The light receiving section  57  receives an infrared signal transmitted from the controller RC, decodes the infrared signal thus received, and then outputs the result to the input processing section  59 . The operation panel  58  has buttons and switches for performing ON/OFF of the power and a variety of operations of the projector  5 . The input processing section generates the information representing the operation content by the controller RC or the operation panel  58 , and then outputs the information to the CPU  50 . 
     In the projector  5 , the CPU  50  executing the program is an example of the coordinate data generation section  506 , the coordinate conversion sections  507 ,  509 , the integration section  510 , the image data acquisition section  512 , and the image compression section  513 . The IF section  53 , which is controlled by the CPU  50  executing the program, is an example of the video signal acquisition section  501 , the coordinate data acquisition section  508 , the coordinate data output section  511 , and the image data output section  514 . The image processing circuit  54 , which is controlled by the CPU  50  executing the program, is an example of the image adjustment section  502  and the image processing section  503 . The projection unit  55 , which is controlled by the CPU  50  executing the program, is an example of the projection section  504 . The image sensors  56 , which are controlled by the CPU  50  executing the program, are an example of the imaging section  505 . 
     The hardware configuration of the PC  2  is substantially the same as shown in  FIG. 4  related to the first embodiment. Therefore, the graphical description thereof will be omitted. The hardware configuration of the tablet terminal  3  is substantially the same as shown in  FIG. 5  related to the first embodiment. Therefore, the graphical description thereof will be omitted. 
       FIG. 14  is a block diagram showing a hardware configuration of the pointing body  6 . The pointing body  6  includes a control section  60 , a pressure sensor  61 , and an LED  62 . The control section  60  is a control device for controlling the action of each of the sections of the pointing body  6 . The pressure sensor  61  is disposed at the tip of the pointing body  6 , and detects the pressure to the tip of the pointing body  6 . The LED  62  outputs light with a wavelength unique to the pointing body  6 . In the pointing body  6 , the pressure sensor  61  controlled by the control section  60  is an example of the pressure detection section  601 . The LED  62  controlled by the control section  60  is an example of the light emitting section  602 . 
       FIG. 15  is a sequence chart showing a process executed in the projection system PS3. In this example, the PC  2  executes a drawing program for drawing a picture on the input image (here, the image displayed on the display section  24 ). In such a circumstance, in the case of attempting to perform drawing on the input image (and the projection image), there can be cited a method of operating the input section  25  (e.g., the mouse) of the PC  2 , and a method of performing a writing action using the pointing body  6 . However, in the method of operating the input section  25  of the PC  2 , since the projector  5  and the PC  2  are connected to each other with the wired connection, there arises a distance limitation in performing the drawing in a place distant from the projector  5 . Further, in the method of performing the writing action using the pointing body  6 , since it is necessary to have direct contact with the projection image projected on the screen SC, it is unachievable to perform the drawing in a place distant from the screen SC. The projection system PS3 makes the tablet terminal  3  function as a pointing device for operating the PC  2  to thereby suppress the distance limitation in performing the drawing. The process shown in  FIG. 15  is triggered by, for example, the fact that the PC  2  outputs the video signal (here, the video signal representing the primary image) to the projector  5 . It should be noted that the case in which the writing action using the pointing body  6  and the operation of the tablet terminal  3  are both performed by the respective users different from each other will hereinafter be explained as an example. 
     In the step SC 1 , the CPU  50  of the projector  5  obtains the video signal from the PC  2 . In the step SC 2 , the CPU  50  performs the resizing process on the input image. The resizing process is substantially the same as the resizing process explained with reference to  FIG. 7  related to the first embodiment. Due to the resizing process, the offset value α and the conversion coefficient β are calculated. Due to the resizing process, the CPU  50  changes the size of the input image to a size corresponding to the liquid crystal panels  552 . 
     In the step SC 3 , the CPU  50  compresses the image data representing the resized image. Specifically, the CPU  50  reads out the image data from the frame memory  52   a  to thereby obtain the image data, and then compresses the image data so as to correspond to the frequency band of the wireless LAN. The CPU  50  compresses the image data using, for example, the JPEG method. The compression of the image data is performed, for example, every several frames, or every predetermined period of time. The CPU  50  stores the compressed image data in the RAM  52 . In the step SC 4 , the CPU  50  reads out the compressed image data from the RAM  52  and then outputs the image data to the tablet terminal  3 . 
     In the step SC 5 , the CPU  50  performs the image processing on the resized image. Specifically, the CPU  50  reads out the image data from the frame memory  52   a , and then performs predetermined image processing (e.g., a process of superimposing an OSD image, a keystone distortion correction process, a frame rate conversion process, and an overdrive process) on the resized image. The CPU  50  writes the image data representing the resized image (the projection image), on which the image processing has been performed, in the frame memory  52   b . In the step SC 6 , the CPU  50  drives the liquid crystal panels  552  in accordance with the image data stored in the frame memory  52   b . Specifically, the CPU  50  reads out the image data from the frame memory  52   b , and then outputs the image data to the panel drive circuit  555 . 
     In the step SC 7 , the CPU  50  detects that the writing action using the pointing body  6  has been performed on the projection image projected on the screen SC. Specifically, the CPU  50  controls the image sensors  56  to perform imaging at predetermined time intervals (e.g., every 0.1 second). The CPU  50  analyzes the image data representing the image thus taken, and then detects the light output from the pointing body  6  to thereby detect the writing action. In the step SC 8 , the CPU  50  generates the pen input data. Specifically, the CPU  50  calculates the coordinate of the point pointed by the pointing body  6  on the projection image based on the position of the light in the image thus taken. The CPU  50  stores the pen input data thus generated in the RAM  52 . The process in the step SC 8  is performed every time the writing action is detected, and a plurality of pen input data is generated sequentially. 
     In the step SC 9 , the CPU  50  performs the coordinate conversion process on the pen input data. The coordinate conversion process denotes a process of converting the coordinate system of the coordinate represented by the coordinate data into the coordinate system of the input image. Here, the CPU  50  converts the coordinate system of the coordinate of the projection image represented by the pen input data into the coordinate system of the (original) input image on which the resizing process has not yet been performed. The specific process is as follows. Firstly, the CPU  50  converts the coordinate on the projection image represented by the pen input data into the coordinate on the resized image. The conversion between the coordinate on the projection image and the coordinate on the resized image is performed using a formula determined in accordance with the content of the image processing performed in the step SC 5 . For example, in the case in which the keystone distortion correction process is performed on the resized image in the step SC 5 , the CPU  50  performs a process of performing the reverse conversion of the keystone distortion correction process to thereby convert the coordinate on the projection image into the coordinate on the resized image. Then, the CPU  50  converts the coordinate on the resized image, on which the conversion has been performed, into the coordinate in the original input image. The conversion between the coordinate (Xi, Xi) on the resized image and the coordinate (xi, yi) on the original input image is performed with Formula (5) described with respect to the first embodiment using the offset value α and the conversion coefficient β stored in the RAM  52  due to the resizing process. 
     The CPU  50  stores the converted coordinate (xi, yi) in the RAM  52 . 
     In the step SC 10 , the CPU  30  of the tablet terminal  3  displays the image, which corresponds to the resized image represented by the image data obtained from the projector  5 , on the touch panel  34 . Specifically, the CPU  30  changes the size of the resized image represented by the image data to a size corresponding to the touch panel  34 , and then displays the resized image, which has been changed in size, on the touch panel  34 . Due to the processing in the step SC 10 , the image corresponding to the projection image is displayed on the touch panel  34 . In the step SC 11 , the CPU  30  generates the touch input data. Specifically, the CPU  30  converts the physical coordinate of the point pointed by the user on the touch panel into the coordinate of a point on the resized image represented by the image data. The process in the step SC 11  is triggered by the fact that the touch panel  34  detects the operation by the user. The conversion between the physical coordinate on the touch panel  34  and the coordinate of the point on the resized image is performed using a predetermined formula. The CPU  30  stores the touch input data thus generated in the RAM  32 . In the step SC 12 , the CPU  30  reads out the touch input data from the RAM  32  and then outputs the touch input data to the projector  5 . It should be noted that the processes in the steps SC 11  and SC 12  are performed every time the touch panel  34  detects the operation by the user, and the plurality of touch input data is sequentially output to the projector  5 . 
     In the step SC 13 , the CPU  50  of the projector  5  performs the coordinate conversion process on the touch input data obtained from the tablet terminal  3 . Here, the CPU  50  converts the coordinate system of the coordinate of the resized image represented by the touch input data into the coordinate system of the original input image. Specifically, the CPU  50  converts the coordinate (Xi, Yi) on the resized image represented by the touch input data into the coordinate (xi, yi) in the original input image using Formula (5) described with respect to the first embodiment. For example, in the example of the size described above, in the case in which the coordinate (Xi, Yi) represented by the touch input data is (275, 480), the coordinate (xi, yi) in the original input image becomes (500, 500). The CPU  50  stores the converted coordinate (xi, yi) in the RAM  52 . It should be noted that the coordinate (xi, yi) (hereinafter referred to as a “pen input coordinate”) obtained by the coordinate conversion process (the step SC 9 ) on the pen input data, and the coordinate (xi, yi) (hereinafter referred to as a “touch input coordinate”) obtained by the coordinate conversion process (the step SC 13 ) on the touch input data are stored in the RAM  52  in a state of being distinguished from each other using respective identifiers different from each other. In other words, the pen input coordinate based on the pen input data and the touch input coordinate based on the touch input data are distinguished from each other using the respective identifiers different from each other. 
     In the step SC 14 , the CPU  50  integrates the pen input data and the touch input data with each other to generate the integrated coordinate data. The integration of the pen input data and the touch input data is performed in response to, for example, selection of either one of the pen input coordinate and the touch input coordinate. The CPU  50  selects the coordinate obtained by either one of the series of writing actions using the pointing body  6  and the series of operations of the touch panel  34 , which starts earlier. Here, the series of writing actions using the pointing body  6  denotes the action of the user from pressing the tip of the pointing body  6  against the screen SC to releasing the tip, or a cluster of a plurality of such actions in which the user separates the tip of the pointing body  6  from the screen SC for a time shorter than a predetermined time. The series of operations of the touch panel  34  denotes the action of the user from touching the touch panel  34  to separating therefrom, or a cluster of a plurality of such actions in which the user does not touch the touch panel  34  for a time shorter than a predetermined time. When either one of the series of writing actions using the pointing body  6  or the series of operations of the touch panel  34  is started in the state in which neither the input from the pointing body  6  nor the input from the touch panel  34  exists, the coordinate obtained by the one of the series of the writing actions and the series of operations is selected until the one of the series of the writing actions and the series of operations is terminated. The state in which no input from the pointing body  6  exists denotes the state in which the user separates the tip of the pointing body  6  for a time equal to or longer than the predetermined time. The state in which no input from the touch panel  34  exists denotes the state in which the user does not touch the touch panel  34  for a time equal to or longer than the predetermined time. In the example shown in  FIG. 15 , the series of writing actions using the pointing body  6  is started prior to the series of operations of the touch panel  34 , and therefore, the CPU  50  selects the pen input coordinate. The CPU  50  stores the integrated coordinate data thus generated in the RAM  52 . In the step SC 15 , the CPU  50  reads out the integrated coordinate data from the RAM  52  and then outputs the integrated coordinate data to the PC  2 . 
     In the step SC 16 , the CPU  20  of the PC  2  draws a picture corresponding to the integrated coordinate data obtained from the projector  5  on the primary image. Specifically, the CPU  20  interpolates the plurality of coordinates (xi, yi) (hereinafter referred to as “integrated coordinates”) represented by the integrated coordinate data to thereby draw the picture (hereinafter referred to as a “trajectory image”) corresponding to the trajectory of the point, which the user has pointed with the pointing body  6  on the screen SC (on the projection surface), or the point, which the user has pointed on the touch panel  34 . The CPU  20  stores the sequence, in which the integrated coordinates sequentially output from the projector  5  are obtained, in the RAM  22 , and forms the image by connecting the plurality of integrated coordinates to each other along the sequence while interpolating the coordinates as the trajectory image. The sequence in which the integrated coordinates are obtained is stored in the RAM  22  together with the integrated coordinates when the CPU  20  obtains the integrated coordinate data from the projector  5 . Then, the CPU  20  combines the trajectory image and the primary image with each other to generate the secondary image. The CPU  20  stores the image data representing the secondary image into the RAM  22 . In the step SC 17 , the CPU  20  reads out the image data representing the secondary image from the RAM  22 , and then outputs a video signal representing the image data to the projector  5 . 
     In the steps SC 18  through SC 22 , the CPU  50  of the projector  5  performs substantially the same processes as the processes in the steps SC 2  through SC 6  on the secondary image. Due to the process in the step SC 22 , the projection image based on the secondary image is projected on the screen SC. In the step SC 23 , the CPU  30  of the tablet terminal  3  displays the image, which corresponds to the resized image of the secondary image, on the touch panel  34  using substantially the same process as the process in the step SC 10 . Due to the processes described hereinabove, the tablet terminal  3  can be made to function as a pointing device for operating the PC  2 . Thus, the picture corresponding the writing action using the pointing body  6  or the operation of the touch panel  34  is drawn on the input image (and the projection image). Therefore, in the case of tempting to perform the drawing on the input image, it becomes possible for the user to arbitrarily select the method of performing the writing action using the pointing body  6  and the method of operating the touch panel  34 . According to the method of operating the touch panel  34 , since the drawing can be performed even in the place distant from the screen SC, the distance limitation in performing the drawing can be suppressed. As an application example of the projection system PS3, it is possible that a teacher performs drawing on the input image by performing the writing action on the screen SC, and a student operates the tablet terminal  3  to thereby perform drawing on the input image in a place distant from the screen SC in a classroom of a school. 
     Fourth Embodiment 
       FIG. 16  is a diagram showing an overall configuration of a projection system PS4 according to a fourth embodiment of the invention. Hereinafter, the projection system PS4 will be explained focusing on the different parts from the projection system PS3. In the projection system PS4, AV equipment such as a DVD player  4  is used as the video signal source instead of the PC  2  described above. The DVD player  4  outputs the video signal to the projector  5 . The DVD player  4  is connected to the HDMI terminal of the projector  5  with a cable using wired connection. In the projection system PS4, the projector  5  executes a drawing program for drawing a picture on the input image. In the case in which the projector  5  is executing the drawing program, the tablet terminal  3  functions as the pointing device for operating the projector  5 . When the user operates the touch panel  34 , a picture corresponding to the operation is drawn on the input image in the projector  5 . 
       FIG. 17  is a block diagram showing a functional configuration of the projection system PS4. The projector  5  has a drawing section  515  and a combination section  516  instead of the coordinate conversion section  509  and the coordinate data output section  511  shown in  FIG. 12 . The drawing section  515  draws the picture corresponding to the integrated coordinate data generated by the integration section  510 . The combination section  516  combines the picture drawn by the drawing section  515  and the resized image of the primary image with each other to generate image data representing the secondary image. The image processing section  503  performs predetermined image processing on the secondary image represented by the image data generated by the combination section  516 . The image processing section  503  outputs the secondary image, on which the image processing has been performed, to the projection section  504 . The image data acquisition section  512  obtains the image data generated by the combination section  516 . It should be noted that in the projection system PS4, the coordinate conversion section  507  converts a coordinate system of the coordinate represented by the pen input data generated by the coordinate data generation section  506  into a coordinate system of the resized image. In the projector  5  according to the fourth embodiment, the CPU  50  executing the program is an example of the coordinate data generation section  506 , the coordinate conversion section  507 , the integration section  510 , the image data acquisition section  512 , the image compression section  513 , the drawing section  515 , and the combination section  516 . 
       FIG. 18  is a sequence chart showing a process executed in the projection system PS4. The following process is triggered by the fact that an instruction for making the projector  5  execute the drawing program is input to the projector  5  in a state in which the DVD player  4  is outputting the video signal (here, the video signal representing the primary image) to the projector  5 . The instruction for executing the drawing program is input in response to the user operating the controller RC. 
     In the step SD 1 , the CPU  50  of the projector  5  obtains the video signal from the DVD player  4 . In the steps SD 2  through SD 8 , the CPU  50  performs substantially the same processes as in the steps SC 2  through SC 8 . 
     In the step SD 9 , the CPU  50  converts the coordinate on the projection image represented by the pen input data into the coordinate on the resized image. The conversion between the coordinate on the projection image and the coordinate on the resized image is performed using a formula determined in accordance with the content of the image processing performed in the step SD 5 . The CPU  50  stores the coordinate (Xi, Yi) on the resized image, on which the conversion has been performed, in the RAM  52 . 
     In the steps SD 10  through SD 12 , the CPU  30  of the tablet terminal  3  performs substantially the same processes as in the steps SC 10  through SC 12 . In the step SD 13 , the CPU  50  of the projector  5  integrates the pen input data and the touch input data with each other to generate the integrated coordinate data. It should be noted that the pen input data and the touch input data integrated with each other in the step SD 13  each represent the coordinate (Xi, Yi) on the resized image, and the integrated coordinate represented by the integrated coordinate data also represents the coordinate (Xi, Yi) on the resized image. In the step SD 14 , the CPU  50  draws the picture corresponding to the integrated coordinate data. Specifically, the CPU  50  interpolates a plurality of integrated coordinates (Xi, Yi) to thereby draw the trajectory image. The CPU  50  stores the trajectory image into the RAM  52 . In the step SD 15 , the CPU  50  combines the trajectory image and the resized image of the primary image with each other to generate the secondary image. Specifically, the CPU  50  respectively reads out the resized image of the primary image from the frame memory  52   a , and the trajectory image from the RAM  52 , to combine (overlay) the trajectory image on the resized image. The CPU  50  writes the image data representing the secondary image thus generated in the frame memory  52   a.    
     In the steps SD 16  through SD 19 , the CPU  50  performs substantially the same process as in the steps SD 3  through SD 6 . Due to the processes described hereinabove, the tablet terminal  3  can be made to function as a pointing device for operating the projector  5 . Thus, the picture corresponding to the writing action using the pointing body  6  or the operation of the touch panel  34  is drawn on the input image (and the projection image). According to the method of operating the touch panel  34 , since the drawing can be performed even in the place distant from the screen SC, the distance limitation in performing the drawing can be suppressed. 
     MODIFIED EXAMPLES 
     The invention is not limited to the embodiments described above, but can be put into practice with a variety of modifications. Hereinafter, some modified examples will be explained. It is also possible to use two or more of the modified examples explained hereinafter in combination. 
     1. Modified Example 1 
     The processes performed in the projection system are not limited to the processes explained in the description of the embodiments. For example, the compression of the image data can also be performed every frame. 
     Further, in the above description of the embodiments, there is explained the example in which the image data on which the image processing has not been performed is read out from the frame memory, and the image data thus read out is output to the tablet terminal  3 . In this respect, it is also possible that the image data on which the image processing has already been performed is readout from the frame memory, and the image data, which is obtained by performing the predetermined process on the image data thus read out, is output to the tablet terminal  3 . For example, in the case of performing the keystone distortion correction process on the resized image, it is also possible for the CPU  10  and the CPU  50  to perform a process of performing the reverse conversion of the keystone distortion correction process on the image data on which the keystone distortion correction process has been performed, and then output the image data, on which the reverse conversion has been performed, to the tablet terminal  3 . It should be noted that in this case, each of the RAM  12 ,  52  of the projectors  1 ,  5  is not necessarily required to have two frame memories. 
     Further, although in the above description of the embodiments, there is explained the example in which the picture corresponding to the coordinate data is drawn on the primary image, it is also possible to further draw the picture corresponding to the coordinate data on the secondary image. 
     2. Modified Example 2 
     In the above description of the embodiments, there is explained the example of calculating the offset value α and the conversion coefficient β every frame in the resizing process. In this respect, during a period in which the video signal is continuously input to the projectors  1 ,  5 , it is also possible to resize the input image using the same values as the offset value α and the conversion coefficient β once calculated. On this occasion, the CPU  10  and the CPU  50  store the offset value α and the conversion coefficient β once calculated in the RAM  12 ,  52  during the period in which the video signal is continuously input, and resize the plurality of input images using these values. 
     3. Modified Example 3 
     Formulas 1 through 5 described above shown with respect to the resizing process and the coordinate conversion process are illustrative only, and it is also possible to perform the resizing process or the coordinate conversion process using formulas different from these formulas. For example, although in the above description of the embodiments, there is explained the case in which the offset value is the value representing the horizontal number of the pixels uniformly removed from the input image, the offset value can also be a value representing the vertical number of the pixels uniformly removed from the input image. On this occasion, the offset value is calculated using a formula different from Formula (1). Further, although in the above description of the embodiments, there is explained the example of contracting the input image in the resizing process, the input image can also be expanded in the resizing process. 
     4. Modified Example 4 
     Although in the above description of the third and fourth embodiments, there is explained the example in which the integrated coordinate data represents either one of the pen input coordinate (or the coordinate represented by the pen input data; the same applies hereinafter) and the touch input coordinate (or the coordinate represented by the touch input data; the same applies hereinafter). In this respect, it is also possible for the integrated coordinate data to represent both of the pen input coordinate and the touch input coordinate. In this case, the pen input coordinate and the touch input coordinate are stored in the RAM  52  while being distinguished from each other using the respective identifiers different from each other. Further, on this occasion, the identifier for identifying the pen input coordinate and the identifier for identifying the touch input coordinate thus distinguished from each other can also correspond to other input devices of the external device (or the projector  5 ). For example, it is also possible that the PC  2  further includes a touch panel as an input device in addition to the hardware configuration described above, and the identifier for identifying the pen input coordinate corresponds to the mouse of the PC  2 , and the identifier for identifying the touch input coordinate corresponds to the touch panel, respectively. According to this example, when the user performs the writing action using the pointing body  6 , the drawing corresponding to the operation of the mouse of the PC  2  is performed, and when the user operates the touch panel  34 , the drawing corresponding to the operation of the touch panel of the PC  2  is performed. 
     Further, although in the above description of the third and fourth embodiments, there is described the processing example of the case in which the writing action using the pointing body  6  is performed prior to the operation of the touch panel  34 , it is obviously possible that the operation of the touch panel  34  is performed prior to the writing action using the pointing body  6 . In this case, the processes described in the steps SC 7  through SC 9  (the steps SD 7  through SD 9 ) are performed after the processes described in the steps SC 11  through SC 13  (the steps SD 11  and SD 12 ). 
     Further, although in the above description of the embodiments, there is explained the example in which the picture corresponding to the integrated coordinate data is drawn on the primary image, it is also possible to further draw the picture corresponding to the integrated coordinate data on the secondary image. 
     5. Modified Example 5 
     The configuration of the projection system is not limited to the configurations described in the description of the embodiments. For example, although in the description of the first embodiment, there is explained the example in which the IF section  13  of the projector  1  outputs the coordinate data to the PC  2  via the USE terminal, it is also possible for the IF section  13  to output the coordinate data via the wireless LAN interface. In another example, it is also possible to use a plurality of tablet terminals  3  or a plurality of pointing bodies  6  in the projection system. In this case, the touch input coordinates obtained from the plurality of tablet terminals  3 , or the pen input coordinates obtained from the plurality of pointing bodies  6  can also be distinguished using respective identifiers different from each other. According to this example, there is performed the drawing corresponding to the different input device of the external device (or the projector  1  or  5 ) between the case in which the user operates a certain touch panel  34 , and the case in which the user operates another touch panel  34 . In still another example, a video player can also be used instead of the DVD player  4 . 
     6. Modified Example 6 
     The functional configuration of the projector  1  is not limited to the case of using either one of the configurations respectively shown in  FIGS. 2 and 9 . It is also possible for the projector  1  to include both of the functional configurations shown in  FIGS. 2 and 9 . In this case, the projector  1  performs the process shown in  FIG. 6  in the case in which the input source of the video signal is the PC  2 , or performs the process shown in  FIG. 10  in the case in which the input source of the video signal is the DVD player  4 . 
     7. Modified Example 7 
     The functional configuration of the projector  5  is not limited to the case of using either one of the configurations respectively shown in  FIGS. 12 and 17 . It is also possible for the projector  5  to include both of the functional configurations shown in  FIGS. 12 and 17 . In this case, the projector  5  performs the process shown in  FIG. 15  in the case in which the input source of the video signal is the PC  2  (i.e., the external device for executing the drawing program), or performs the process shown in  FIG. 18  in the case in which the input source of the video signal is the DVD player (i.e., the external device not performing the drawing program). In another example, the imaging section  505  and the coordinate data generation section  506  can also be external constituents of the projector  5 . In this case, the projector  5  has a coordinate data acquisition section for obtaining the pen input data generated by the coordinate data generation section  506 . 
     8. Modified Example 8 
     The hardware configurations of the projector  1 , the PC  2 , and the tablet terminal  3  are not limited to the configurations shown in  FIGS. 3 through 5 . The projector  1 , the PC  2 , and the tablet terminal  3  can have any hardware configurations providing the processes of the respective steps shown in  FIGS. 6, 7, and 10  can be executed. For example, although in the above description of the embodiments, there is explained the example in which the projector  1  has the three liquid crystal panels  152 , the projector  1  can also be configured using a system obtained by combining the single liquid crystal panel  152  and a color wheel with each other, a system using three digital mirror devices (DMD™), a system obtained by combining a single DMD™ and the color wheel with each other, and so on. 
     9. Modified Example 9 
     The hardware configurations of the projector  5  and the pointing body  6  are not limited to the configurations shown in  FIGS. 13 and 14 . The projector  5 , the PC  2 , the tablet terminal  3 , and the pointing body  6  can have any hardware configurations providing the processes of the respective steps shown in  FIGS. 15 and 18  can be executed. For example, although in the above description of the embodiments, there is explained the example in which the projector  5  has the three liquid crystal panels  552 , the projector  5  can also be configured using a system obtained by combining the single liquid crystal panel  552  and a color wheel with each other, a system using three digital mirror devices (DMD™), a system obtained by combining a single DMD™ and the color wheel with each other, and so on. 
     10. Modified Example 10 
     Although in the embodiments described above, the explanation is presented citing the projectors  1 ,  5  as examples of the image display device, the image display device is not limited to the projectors. It is also possible to apply the invention to, for example, a rear projector integrally provided with a transmissive screen, and a flat panel display (FPD) such as a liquid crystal display, a plasma display, or an organic EL display. 
     11. Modified Example 11 
     Although in the above description of the third and fourth embodiments, it is assumed that the pointing body  6  emits the light with a unique wavelength, the invention is not limited to this configuration. For example, it is also possible to arrange to use a radio wave for wireless communication. Further, the pointing body  6  can also be a finger of the user.