Abstract:
Structure and function for inputting information preferably includes a display device having two cameras in respective corners thereof. At least one computer readable medium preferably has program instructions configured to cause at least one processing structure to: (i) extract an object located on a plane of the display device from an image that includes the plane of the object, (ii) determine whether the object is a writing implement by determining, when a plurality of objects are extracted from the image, that one of the plurality of objects that satisfies a prescribed condition is the writing implement, (iii) calculate a position of a contact point between the writing implement and the plane as information to be input if the object has been determined as the writing implement, and (iv) input the information representing a position on the plane indicated by the object.

Description:
This application is a continuation of U.S. patent application Ser. No. 12/788,822, filed May 27, 2010 (now U.S. Pat. No. Re. 42,794, issued Oct. 4, 2011), which is a reissue of U.S. patent application Ser. No. 10/976,990, filed Nov. 1, 2004, now U.S. Pat. No. 7,379,622, which is a divisional of U.S. patent application Ser. No. 09/742,063, filed Dec. 22, 2000, now U.S. Pat. No. 6,829,372, the contents of all are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an information-inputting device that can record data in a recording medium in real time while the data is being written on a recording surface without specifying types of writing implements and materials used for the recording surface. 
     2. Description of the Related Art 
     Methods and apparatuses for inputting information have been proposed, and have been put to practical use. For instance, Japanese Laid-open Patent Application No. 6-289989 discloses an information recognition device. The information recognition device provides a camera on one side of a recording surface. The information recognition device detects coordinates of each position of information recorded by a writing implement on the recording surface, for example, a track of letters written on recording paper, and develops depiction data based on the coordinates. The information recognition device alternatively detects coordinates of each position of a writing implement, that is, coordinates of a tip of the writing implement, and develops depiction data based on the coordinates. To recognize the information recorded on the recording surface, the information recognition device also needs to detect the origin of the coordinates on the recording surface by detecting corners of the recording paper, that is, the recording surface, and the origin of the X-axis and the Y-axis recorded on the recording paper. 
     The information recognition device must detect the corners of the recording paper or the origin of the coordinates based on the information recorded on the recording paper before detecting the coordinates of each position of the information every time the recording paper is exchanged. Additionally, in a case that a position of the recording paper is moved from its original position while recording the information on the recording paper, or in a case that positions of the corners of the recording paper in an image being taken by the camera are moved. coordinates of recording the information on the recording paper are detected by the camera as different coordinates from what they are supposed to be, since the coordinates of recording the information are calculated based on the origin of the coordinates. Consequently, the camera detects different information from what a user intends to record unless a moved origin of the coordinates is detected. 
     Additionally, when the camera photographs the information recorded on the recording paper from an upper oblique direction of the recording paper, error between actual coordinates of the information recorded on the recording paper and coordinates detected by the camera increases as a distance between the recording paper and the camera increases. Such a problem will be described with reference to  FIGS. 1A and 1B . An angle θ indicates an angle range that a fixed number of pixels provided in the vertical direction of an imaging device such as the camera can detect light through a lens. In  FIG. 1A , a distance on the recording paper that the imaging device can detect with the angle θ is a distance L 1 . In  FIG. 1B , a distance on the recording paper that the imaging device can detect with the angle θ is a distance L 2 . It is assumed that the distance L 2  is greater than the distance L 1 . Accordingly, the greater the distance between the recording paper and the camera, the wider an area on the recording paper that can be detected by the camera with the angle θ. In other words, an area on the recording paper detected by each pixel that is provided in the imaging device increases as the distance between the recording paper and the camera increases. Accordingly, when the camera photographs the information recorded on the recording paper from the upper oblique direction of the recording paper, the error between the actual coordinates of the information recorded on the recording paper and the coordinates detected by the camera increases as the distance between the recording paper and the camera increases. Thus, an image detected by the camera is contracted with respect to an image corresponding to the information recorded on the recording paper. 
     The number of pixels provided in the imaging device necessary for obtaining image data by photographing the coordinates of each position of the information depends on a size of a recording area on the recording paper and a resolution of reading the coordinates of each position of the information recorded on the recording paper. As the size of the recording area increases, the greater the number of pixels necessary for calculating the coordinates from the image data also increases. Additionally, for a higher resolution of reading the coordinates, the number of pixels must be greater. Furthermore, a frame rate of image signals outputted from the imaging device must be high in order to clearly monitor an information recording process from the photographed image data. However, an imaging device with a large number of pixels and a high frame rate is generally expensive, and thus it is hard to hold down production cost of an information input device by mounting such an imaging device thereon. Consequently, a writing input device with a comparatively inexpensive imaging device using a smaller number of pixels has been requested. 
     Additionally, a size of an image-display device used in a portable writing input device for displaying the image data obtained by the camera is preferred to be small for miniaturization of the device and its electric efficiency. However, if the size of the image-display device is small, the number of pixels displayed on the image-display device becomes small, and thus quality of the image data displayed on the image-display device decreases by stretching the image data immoderately when displaying a page of the image data thereon. Furthermore, when the number of imaging devices used for photographing the information recorded on the recording paper is small, a wide-angle lens should be attached to each of the imaging devices for photographing the information. In such case, a resolution of reading the coordinates of the information recorded on the recording paper differs depending on where the information is recorded on the recording paper. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a general object of the present invention to provide an information-inputting device used for writing data on a recording surface by use of a writing implement. A more specific object of the present invention is to provide an information-inputting device, a writing input device and a portable electronic writing input device that are easily carried and are used for writing data on a desired recorded material whose surface is a plane by use of a desired writing implement. Another object of the present invention is to provide a method and an apparatus for recording data in a recording medium in real time while the data is being written on a recording surface by use of a writing implement in a case in which the writing implement is detected. Yet, another object of the present invention is to provide a method of managing written data and a recording medium for creating a page of the written data by dividing the written data into a plurality of parts and by inputting the plurality of parts by a recording area in a case in which a resolution of reading the written data in the recording area is low. Yet, another object of the present invention is to provide a method of managing written data and a recording medium for controlling a pixel density of the written data to be even throughout an entire recording area. Yet, another object of the present invention is to provide a method of controlling display of a recording area to increase operability of writing data in the recording area. 
     The above-described objects of the present invention are achieved by an information-inputting device including a plurality of photographing units photographing an area on a plane; an object-recognizing unit extracting an object located on the plane from a photographed image, and recognizing whether the object is a specific object; a location-calculating unit calculating a contact position of the specific object on the plane from the photographed image if the object has been recognized as the specific object; and a data-storing unit storing information about a track of the contact position while the specific object is contacting the plane. 
     The above-described objects of the present invention are also achieved by a method of inputting information including the steps of extracting an object located on a plane from an image that includes the plane and the object; recognizing whether the object is a specific object; and inputting a contact position of the specific object on the plane as information if the object has been recognized as the specific object. 
     The above-described objects of the present invention are also achieved by a writing input device including an image-inputting unit photographing a recording area on a plane by providing a plurality of electronic cameras that include imaging devices; an object-recognizing unit extracting an object located on the plane from a photographed image, and determining whether the object is a writing implement by recognizing a shape of the object; a coordinate-calculating unit calculating contact coordinates of the object on the plane based on an image of the object on an imaging device if the object has been determined as the writing implement; a data-storing unit storing a series of the contact coordinates while the object is contacting the plane; and a displaying unit creating depiction data from the series of the contact coordinates, and displaying the depiction data thereon. 
     The above-described objects of the present invention are also achieved by a method of managing written data in a writing input device, wherein the writing input device includes an image-inputting unit photographing a recording area on a plane by providing a plurality of electronic cameras that includes imaging devices; an object-recognizing unit extracting an object located on the plane from a photographed image, and determining whether the object is a writing implement by recognizing a shape of the object; a coordinate-calculating unit calculating contact coordinates of the object on the plane based on an image of the object on an imaging device if the object has been determined as the writing implement; a data-storing unit storing a series of the contact coordinates while the object is contacting the plane; and a displaying unit creating depiction data from the series of the contact coordinates, and displaying the depiction data thereon, the method including the steps of dividing a page of a data area into a plurality of areas; assigning one of the areas to the recording area; and managing the written data to be recorded in the recording area as data of the one of the areas in the page. 
     The above-described objects of the present invention are also achieved by a portable electronic writing input device including a main body unit; a first camera unit; a second camera unit; and an expansion/contraction unit connecting the first and second camera units on left and right parts of the main body unit as well as expanding or contracting an interval between the main body unit and the first or second camera unit, wherein the portable electronic writing input device, being placed on a plane material, photographs a movement of a writing implement by use of the first and second camera units, when a user writes data on the plane material by using the writing implement. 
     The above-described objects of the present invention are also achieved by a recording medium readable by a computer, tangibly embodying a program of instructions executable by the computer to perform a method, the method including the steps of extracting an object located on a plane from an image including the object and the plane; recognizing whether the object is a specific object; calculating a contact position of the specific object on the plane if the object has been recognized as the specific object; storing written data including a series of coordinates of the contact position calculated while the object is contacting the plane; generating depiction data from the written data; and displaying the depiction data. 
     The information-inputting device determines a shape of the object on the plane by use of the object-recognizing unit, and calculates the contact positions of the specific object by use of the location-calculating unit if the object has been determined as the specific object by the object-recognizing unit. Subsequently, the information-inputting device stores the track of the contact position while the specific object is contacting the plane. Thus, the information-inputting device can record data in a recording medium in real time while the data is being written on a recording surface without specifying types of writing implements and materials used for the recording surface. 
     Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are diagrams used for describing a situation in which an error between actual coordinates of information recorded on recording paper and coordinates detected by a camera increases as distance between the recording paper and the camera increases when the camera photographs the information recorded on the recording paper from an upper oblique direction of the recording paper; 
         FIG. 2  is a diagram showing an appearance of a writing input device according to the present invention; 
         FIG. 3  is a block diagram showing a structure of a camera unit provided in the writing input device; 
         FIG. 4  is a block diagram showing a recording area where the writing input device can obtain coordinates of information recorded thereon; 
         FIG. 5  is a block diagram showing a system structure of the writing input device according to the present invention; 
         FIG. 6  is a diagram for describing a method to obtain coordinates of a contact point of a writing implement contacting the recording area; 
         FIG. 7  is a diagram showing an enlargement of an area where a wide-angle lens and a CMOS image sensor are placed in  FIG. 6 ; 
         FIG. 8  is a flowchart describing steps performed by the writing input device according to a first embodiment of the present invention; 
         FIG. 9  is a diagram showing an image wherein a standard line is rotating around center of gravity of the writing implement; 
         FIG. 10  is a diagram showing an image of the writing implement having symmetry with respect to an axis of symmetry; 
         FIG. 11  is a diagram showing an image wherein the writing implement is contacting a recording surface; 
         FIG. 12  is a flowchart describing steps performed by the writing input device according to a second embodiment of the present invention; 
         FIG. 13  is a flowchart describing steps performed by the writing input device according to a third embodiment of the present invention; 
         FIGS. 14A ,  14 B and  14 C are diagrams showing icons corresponding to typical writing implements; 
         FIG. 15  is a flowchart describing steps performed by the writing input device according to a fourth embodiment of the present invention; 
         FIG. 16  is a flowchart describing steps performed by the writing input device according to a fifth embodiment of the present invention; 
         FIG. 17  is a diagram showing a case in which the writing input device recognizes a plurality of writing implements; 
         FIG. 18  is a flowchart describing steps performed by the writing input device according to a sixth embodiment of the present invention; 
         FIG. 19  is a diagram showing a method of obtaining a valid contact point from a plurality of contact points when a plurality of writing implements are contacting the recording surface; 
         FIG. 20  is a flowchart describing steps performed by the writing input device according to a seventh embodiment of the present invention; 
         FIG. 21  is a flowchart describing steps performed by the writing input device according to an eighth embodiment of the present invention; 
         FIG. 22  is a flowchart describing steps performed by the writing input device according to a ninth embodiment of the present invention; 
         FIG. 23  is a diagram showing the recording area set by a user operation; 
         FIG. 24  is a flowchart describing steps performed by the writing input device according to a tenth embodiment of the present invention; 
         FIG. 25  is a block diagram showing the recording area created by use of a frame; 
         FIG. 26  is a diagram used for describing that a resolution of reading information written in the recording area varies depending on a distance from the camera unit; 
         FIG. 27  is a block diagram showing a method of dividing a page of a data area into displaying blocks; 
         FIG. 28  is a block diagram showing a method of dividing a page of the data area into writing blocks; 
         FIG. 29  is a block diagram showing a relation between a page of the data area and the recording area; 
         FIG. 30  is a flowchart describing steps performed by the writing input device according to a thirteenth embodiment of the present invention; 
         FIG. 31  is a block diagram showing a method of assigning a pixel-displaying area and a displaying area for writing to desired locations in a page of the data area; 
         FIGS. 32A and 32B  are diagrams showing an accentuated displaying area for writing; 
         FIG. 33  is a flowchart describing steps performed by the writing input device according to a sixteenth embodiment of the present invention; 
         FIG. 34  is a diagram showing a location of a writing block displayed on a LCD; 
         FIG. 35  is a flowchart describing steps performed by the writing input device according to a seventeenth embodiment of the present invention; 
         FIG. 36  is a diagram showing the writing block shown in  FIG. 34  after being moved by use of a direction-specifying key; 
         FIG. 37  is a flowchart describing steps performed by the writing input device according to an eighteenth embodiment of the present invention; 
         FIG. 38  is a block diagram showing the pixel-displaying area and a summarized location of the pixel-displaying area in a page of the data area; 
         FIG. 39  is a block diagram showing the displaying area for writing after being moved from a position shown in  FIG. 38  to a left edge of the pixel-displaying area by use of the direction-specifying key; 
         FIG. 40  is a diagram used for describing a method of calculating a resolution of reading coordinates in the recording area; 
         FIGS. 41A and 41B  are diagrams showing directions of writing data; 
         FIG. 42  is a flowchart describing steps performed by the writing input device according to a nineteenth embodiment of the present invention; and 
         FIG. 43  is a block diagram showing a system wherein the present invention is implemented by use of software. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description will now be given of preferred embodiments of the present invention, with reference to the accompanying drawings. 
       FIG. 2  is a diagram showing an appearance of a writing input device according to the present invention. A writing input device  1  shown in  FIG. 2  includes a left camera unit  2 , a right camera unit  3 , photographing windows  4  and  5 , expansion/contraction units  6  and  7 , an LCD (Liquid Crystal Display)  8 , and LEDs (Light-Emitting Diodes)  9  through  12 . The writing input device  1  recognizes a shape of an object from an object image photographed by the left camera unit  2  and the right camera unit  3 , obtains coordinates of the object, and records the coordinates of the object as data in a recording medium. The writing input device  1  is portable, and is placed on a flat recording surface such as a surface of a table or a surface of paper provided on the table, as shown in  FIG. 2 . A recording area  13  facing the left camera unit  2  and the right camera unit  3  is then formed. An optical axis of light entering into the camera units  2  and  3  is parallel to the recording surface, and the light is inputted to the writing input device  1  through the photographing windows  4  and  5 , which are transparent plates. The light entering the writing input device  1  is photographed by an imaging device provided in the writing input device  1  after being reflected by a mirror and passing through a wide-angle lens also provided therein. In the present invention, a CMOS (Complementary Metal Oxide Semiconductor) image sensor is used as the imaging device, for instance. 
     The expansion/contraction units  6  and  7  are expanded and contracted by hand operations, and adjust a distance between the left camera unit  2  and the right camera unit  3 . The LCD  8  displays information such as letters that are written in the recording area  13 . Additionally, the LCD  8  includes various buttons used for its operations, but the buttons are not shown in  FIG. 2 . The LED  9  is provided on an area above the photographing window  4 . The LED  10  is provided on an area above the photographing window  5 . The LED  11  and the LED  12  are provided on an area below the LCD  8 . The LEDs  9  though  12  are used for illuminating the recording area  13 . The above-described LEDs  9  through  12  can be provided on other areas as long as they can illuminate the recording area  13 . 
       FIG. 3  is a block diagram showing a structure of the left camera unit  2 .  FIG. 3  more particularly shows the structure of the left camera unit  2  seen from the side. Both of the left camera unit  2  and the right camera unit  3  have the same structure. The camera unit  2  includes a mirror  14 , a wide-angle lens  15 , a CMOS image sensor  16  and an image-processing circuit  17 , as shown in  FIG. 3 . Light with its optical axis parallel to the recording surface enters the writing input device  1  through the photographing window  4 , and is reflected by the mirror  14  toward the wide-angle lens  15 . The light then arrives at the CMOS image sensor  16  through the wide-angle lens  15 . The CMOS image sensor  16  executes photoelectric conversion on the received light to create an electric signal by rise of a photo-diode provided in each pixel. Subsequently, the CMOS image sensor  16  amplifies the electric signal by use of a cell amplifier used for each pixel, and transmits the amplified signal to the image-processing unit  17  every time a fixed period passes. 
       FIG. 4  is a block diagram showing a recording area where the writing input device  1  can obtain coordinates of information recorded thereon.  FIG. 4  shows the writing input device  1  and the recording surface seen from above. The recording area  13  is shown in a shaded area in  FIG. 4 . A recording position, that is, a position of a writing implement touching the recording surface, can be calculated by using trigonometry from images photographed by the left camera unit  2  and the right camera unit  3 , and thus the recording area  13  wherein coordinates of the recording position can be obtained is an area on the recording surface where a photographing area of the left camera unit  2  and a photographing area of the right camera unit  3  overlap. In other words, an area surrounded by broken lines is the recording area  13 . A lower boundary of the recording area  13  shown in  FIG. 4  is a lowest position of the writing implement where the left camera unit  2  and the right camera unit  3  can detect the position of the writing implement.  FIG. 4  also shows the mirror  14  included in the left camera unit  2  and a mirror  19  included in the right camera unit  3 . The mirror  14  is placed in the left camera unit  2  in order to reflect incident light of about a 90-degree range entering from the photographing window  4 , and to transmit the incident light to the CMOS image sensor  16  through the wide-angle lens  15 . Similarly, the mirror  19  is placed in the right camera unit  3  in order to reflect incident light having about 90 degrees range and entering from the photographing window  5 , and to irradiate the incident light to a later-mentioned CMOS image sensor  21  through a later-mentioned wide-angle lens  20 . 
       FIG. 5  is a block diagram showing a system structure of the writing input device  1 . The writing input device  1  includes the left camera unit  2 , the right camera unit  3 , a CPU (Central Processing Unit)  23  or a processing unit  23 , a ROM (Read-Only Memory)  24 , a main memory  25 , a flash memory  26 , an operation unit  27 , an LCD display-control unit  28 , a USB (Universal Serial Bus) driver  29 , a sound source  30 , the LCD  8 , a USB interface (I/F)  31 , a speaker  32 , a DC-DC converter  33 , a battery  34 , the LED  11 , the LED  12 , and a system bus  35 . The left camera unit  2  includes the mirror  14 , the wide-angle lens  15 , the CMOS image sensor  16 , the image-processing circuit  17 , and the LED  9 . The right camera unit  3  includes the mirror  19 , the wide-angle lens  20 , the CMOS image sensor  21 , an image-processing circuit  22 , and the LED  10 . 
     The mirror  14  reflects incident light entering through the photographing window  4  toward the wide-angle lens  15 . The wide-angle lens  15  having a view angle of 90 degrees is placed in the left camera unit  2  to transmit the light reflected by the mirror  14  to the CMOS image sensor  16 . The CMOS image sensor  16  executes photoelectric conversion on the light received through the wide-angle lens  15  to an analog signal by use of a photo-diode provided for each pixel therein, amplifies the analog signal by using a cell amplifier provided for each pixel, and outputs the amplified analog signal to the image-processing unit  17  every time a fixed period passes. Similarly, in the right camera unit  3 , the mirror  19  reflects incident light entering through the photographing window  5  toward the wide-angle lens  20 . The wide-angle lens  20  having a view angle of 90 degrees is placed in the right camera unit  3  to transmit the light reflected by the mirror  19  to the CMOS image sensor  21 . The CMOS image sensor  21  executes photoelectric conversion on the light received through the wide-angle lens  20  to an analog signal by use of a photo-diode provided for each pixel therein, amplifies the analog signal by using a cell amplifier provided for each pixel, and outputs the amplified analog signal to the image-processing unit  22  every time a fixed period passes. 
     Each of the image-processing circuits  17  and  22  includes an A/D (Analog/Digital) conversion circuit, and converts an analog signal respectively received from the CMOS image sensors  16  and  21  to a digital signal. Subsequently, the image-processing circuits  17  and  22  execute a process to extract an outline of a subject image from image data obtained by converting the analog signal to the digital signal, an image recognition process to decide whether the subject image is a writing implement based on the extracted outline, and a process to output information about a position where an object detected as the writing implement is contacting the recording surface. It should be noted that the left camera unit  2  and the right camera unit  3  perform the above-described processes synchronously with each other. 
     The ROM  24  initially stores a program to control the writing input device  1 . The main memory  25  includes a DRAM (Dynamic Random Access Memory), and is used as a work area for the CPU  23 . The flash memory  26  stores coordinate data, that is, data about the coordinates of the information recorded in the recording area  13 . The operation unit  27  includes various types of keys near the LCD  8 , the keys being used for displaying the coordinate data stored in the flash memory  26  on the LCD  8 , for forwarding the coordinate data to a personal computer through a USB cable, and for other objects. The LCD display-control unit  28  controls displaying of the coordinate data, an operation menu, and the like on the LCD  8 . The USB driver  29  transmits data to a device such as a personal computer connected to a USB cable, and receives data from the device, by executing operations based on a USB standard. The sound source  30  generates a sound signal such as an alarm, and then the generated sound signal is outputted from the speaker  32 . The battery  34  is, for example, a nickel-metal hydride battery or a lithium battery. An electric current is supplied from the battery  34  through the DC-DC converter  33  to units in the writing input device  1  in addition to the LEDs  9  through  12 . The system bus  35  connects the image-processing units  17  and  22 , the CPU  23 , the ROM  24 , the main memory  25 , the flash memory  26 , the operation unit  27 , the LCD display-control unit  28 , the USB driver  29 , and the sound source  30 . 
     A description will now be given of a method to obtain coordinates of a contact point of a writing implement contacting the recording surface. As described with reference to  FIG. 3 , the CMOS image sensors  16  and  21  are placed downwards respectively in the left camera unit  2  and the right camera unit  3 . However, in order to describe the method, it is assumed in  FIG. 6  that the mirrors  14  and  19  are omitted. Additionally, it is assumed that the wide-angle lenses  15  and  20 , and the CMOS image sensors  16  and  21  are placed as shown in  FIG. 6  so that the optical axis of the incident light becomes parallel to the recording surface. A distance between the wide-angle lenses  15  and  20  is named a distance L. The contact point of the writing implement is set as a contact point A. The coordinates of the contact point A are set to (x, y). A straight line connecting the wide-angle lenses  15  and  20  is named a X-Line. An angle between the X-Line and a straight line drawn from the center of the wide-angle lens  15  to the contact point A is named an angle β 1 . An angle between the X-Line and a straight line drawn from the center of the wide-angle lens  20  to the contact point A is named an angle β 2 .  FIG. 7  is a diagram showing an enlargement of an area where the wide-angle lens  15  and the CMOS image sensor  16  are placed in  FIG. 6 . In  FIG. 7 , distances “f” and “h” respectively indicate a distance between the wide-angle lens  15  and the CMOS image sensor  16 , and a distance between an image-formed location of the optical axis  18  of the wide-angle lens  15  and an image-formed location of the contact point A on the CMOS image sensor  16 . An angle α is an angle between the optical axis  18  of the wide-angle lens  15  and the X-Line. An angle θ is an angle between the optical axis  18  of the wide-angle lens  15  and a straight line connecting the contact point A and its image-formed location. The following two equations are derived from  FIGS. 6 and 7 .
 
θ=arctan( h/f )  EQ1
 
β1=α−θ  EQ2
 
     A value of the angle β 1  for the left camera unit  2  can be obtained from the above equations since the angle α is initially measured as an angle for positioning the wide-angle lenses  15  and  20  so that the optical axes of the wide-angle lenses  15  and  20  intersect with each other. Similarly, a value of the angle β 2  can be obtained for the right camera unit  3 . Once the values of the angles β 1  and β 2  have been obtained, the coordinates of the contact point A (x, y) can be obtained by using trigonometry.
 
x= L *tan β2/(tan β1+ tan β2)  EQ3
 
 y=x *tan β1  EQ4
 
     Assuming the mirrors  14  and  19  do not exist in the left camera unit  2  and the right camera unit  3 , the description has been given of the method to calculate the coordinates of the contact point A, that is, the contact point of the writing implement. However, since the mirrors  14  and  19  are provided in the writing input device  1  only for changing a direction of the optical axis placed in each of the left camera unit  2  and the right camera unit  3  by reflecting light on the optical axis, the above-described method can also be applied to calculate the coordinates of the contact point of the writing implement in a case that there are mirrors placed in each of the left camera unit  2  and the right camera unit  3 . As describe above, both an optical axis of light emitted toward the left camera unit  2  and an optical axis of light emitted toward the right camera unit  3  are parallel to a recording surface, and intersect each other. Accordingly, both of the left camera unit  2  and the right camera unit  3  can detect coordinates of a contact point accurately with no errors. In addition, an area where coordinates of the contact point are read by the left camera unit  2  and the right camera unit  3  can be kept wide. 
     A detailed description will now be given of embodiments based on the writing input device  1  according to the present invention. 
     A first embodiment of the present invention relates to a method of storing information as digital data in a recording medium in real time while a user is recording the information by use of a pen on a recorded material such as paper. The first embodiment additionally relates to a method of storing information as digital data in a recording medium in real time while a user is recording the information on the recorded material by use of a writing implement such as a stick or a finger whereto ink is not applied.  FIG. 8  is a flowchart describing steps performed by the writing input device  1  according to the first embodiment of the present invention. The steps shown in  FIG. 8  are actually performed by the image-processing circuits  17  and  22 , and the CPU  23  provided in the writing input device  1 . When a user records or writes information on a recording surface of a recorded material such as paper by use of a writing implement such as a pen, the left camera unit  2  and the right camera unit  3  photograph writing movement performed by the user.  FIG. 9  shows an image of a writing implement  36  photographed by the left camera unit  2  and the right camera unit  3 . 
     The image-processing circuit  17  of the left camera unit  2  converts an analog image signal outputted from the CMOS image sensor  16  into a digital image signal in order to obtain a frame of image data, and extracts an outline of an object from the image data at a step S 101 . In a case that the number of pixels of the CMOS image sensor  16  in a vertical direction (an upward direction of a vertical side  39 ) is large, the image-processing circuit  17  controls outputting image Signals only for pixels of the CMOS image sensor  16  that form an image having a fixed height from a recording surface  38 . An example of the above-described method of extracting the outline of the object is to calculate a density gradient between pixels by applying differentiation, and then to define the outline based on the direction of increasing density gradient and the size of the calculated density gradient. Such method is disclosed in Japanese Laid-open Patent Application No. 63-193282. After the outline has been extracted from the image data, the image-processing circuit  17  determines whether the object is a writing implement or not based on a shape of the extracted outline of the object. An example of image recognition technology to determine the shape of the extracted outline is to obtain a center of gravity  40  of the object, to calculate distances between the center of gravity  40  and points on the outline specified by angles based on the center of gravity  40  in order, and then to define the shape of the extracted outline from relations between the distances and the angles. Such a method is disclosed in Japanese Laid-open Patent Application No. 8-315152. Subsequently, data about the shape of the outline obtained by the above-described method is compared with data that has been stored previously as shapes of writing implements in the ROM  24  or in the flash memory  26  at a step S 102 . Consequently, the object is defined by the image-processing circuit  17  either as a writing implement or as an object other than writing implements at a step S 103 . If the object is detected as the object other than the writing implements, the image-processing circuit  17  proceeds to the step S 101 . 
     Since an angle between the object and the recording surface  38  is not fixed, the data about the object is compared with the data stored in the ROM  24  or the like by rotating a standard line  41  connecting the center of gravity  40  of the object and the outline of the object in an range of certain angles as shown in  FIG. 9  in order to define the shape of the object. A plurality of shapes of writing implements can be provided as the data stored in the ROM  24  or the like, wherein the data about the object can be compared with each of the plurality of shapes of writing implements. Another method of defining the object as a writing implement is to check whether the object is symmetric with respect to an axis of symmetry  42  shown in  FIG. 10 . When the object has been detected as a symmetrical object, the object can be defined as a writing implement. The symmetry of the object can be detected by calculating a distance from the center of gravity  40  to certain points on the outline located around the center of gravity  40  in order. 
     If the object has been detected as a writing implement at the step S 103 , the image-processing circuit  17  determines whether the writing implement has contacted the recording surface  38  as shown in  FIG. 11  at a step S 104 . It should be noted that the recording surface  38  corresponds to a bottom side of a photographing area  37  shown in  FIGS. 9 ,  10  and  11 . Thus, to be concrete, the image-processing circuit  17  checks whether an image of the object in the photographing area  37  touches the bottom side thereof. If it is determined at the step S 104  that the writing implement has not contacted the recording surface  38 , the image-processing circuit proceeds to the step S 101 . If it is determined at the step S 104  that the writing implement has contacted the recording surface  38 , the image-processing circuit  17  obtains the distance “h” between the image-formed locations of the contact point A and the optical axis  18  of the wide-angle lens  15  on the CMOS image sensor  16  at a step S 105 . In  FIG. 11 , the image-formed location of the optical axis  18  of the wide-angle lens  15  is set as a distance “h 0 ” from the bottom left corner of the CMOS image sensor  16 . Additionally, the image-formed location of the contact point A is set as a distance “h 1 ” from the bottom left corner of the CMOS image sensor  16 . Then, the distance “h” can be obtained from the following equation.
 
 h=h 0−h1
 
     It should be noted that the distances “h 0 ” and “h 1 ” can be obtained from the number of pixels counted from the vertical side  39  to the image-formed locations of the optical axis  18  and the contact point A, and a distance between pixels adjacent to each other (a pixel pitch). 
     Once a value of the distance “h” has been calculated, a value of the angle β 1  can be obtained from the equations EQ1 and EQ2 by use of predetermined values of the distance “f” and the angle α at a step S 106 . The angle β 2  can be obtained similarly by taking the above-described steps in the right camera unit  3 . Additionally, at a step S 107 , the coordinates (x, y) of the contact point A on the recording surface can be obtained from the equations EQ3 and EQ4 by use of the values of the angles β 1  and β 2 , and a predetermined value of the distance L. The CPU  23  may execute a calculation using the equations EQ1 through EQ4. Alternatively, the image-processing circuits  17  and  22  may execute a calculation using the equations EQ1 and EQ2. Additionally, the CPU  23  may execute a calculation using the equations EQ3 and EQ4. 
     The CPU  23  creates depiction data, for instance, by connecting each set of coordinates by straight lines based on a series of coordinate data of the contact point A that was obtained while the writing implement  36  was contacting the recording surface  38 . Subsequently, the CPU  23  displays the depiction data on the LCD  8  through the LCD display-control unit  28  at a step S 108 , and stores the series of the coordinate data of the contact point A in the flash memory  26 , for instance, as a single file, at a step S 109 . 
     A description will now be given of a second embodiment of the present invention with reference to  FIG. 12 . The first embodiment describes a case in which the outline of the object is extracted for each frame of the image data after the object has been defined as a writing implement based on the outline of the object. Instead, in the second embodiment, movement of the outline is monitored after the object has been defined as the writing implement, thereby enabling accurate detection of contact of the object with the recording surface  38 . In the second embodiment, an optical flow measurement is applied to a method of detecting the movement of the outline. The optical flow measurement is to measure a velocity vector of each point of an image by using a rate of change in a value of each pixel in a certain period and a rate of change in its surrounding pixels in space. 
       FIG. 12  is a flowchart describing steps performed by the writing input device  1  according to the second embodiment of the present invention. In  FIG. 12 , steps S 201 , S 202  and S 203  respectively correspond to the steps S 101 , S 102  and S 103  shown in  FIG. 8 . At a step S 204 , each of the image-processing circuits  17  and  22  obtains a velocity vector of each point on the outline of the object that has been detected as a writing implement by use of continuous frames of the image data of the writing implement. At a step S 205 , each of the image-processing circuits  17  and  22  checks whether a vector component of the velocity vector in a direction perpendicular to the recording surface  38  has become zero in a case that the writing implement tends to move toward the recording surface  38 . If it is determined at the step S 205  that the vector component has not become zero, the image-processing circuits  17  and  22  proceed to the step S 204 . If it is determined at the step S 205  that the vector component has become zero, each of the image-processing circuits  17  and  22  checks whether the writing implement has contacted the recording surface  38  at a step S 206 . If it is determined at the step S 206  that the writing implement has not contacted the recording surface  38 , the image-processing circuits  17  and  22  proceed to the step S 204 . If it is determined at the step S 207  that the writing implement has contacted the recording surface  38 , the image-processing circuits  17  and  22  proceed to a step S 207 . Steps S 207  through S 211  correspond to the steps S 205  through S 209 , and thus a description of the steps S 207  through S 211  will be omitted. 
     According to the present invention, objects such as a pencil, a stick and a finger may be used as writing implements if they are recognized as writing implements by the writing input device  1 . However, the pencil and the stick that can be writing implements have different shapes. Accordingly, in a third embodiment of the present invention, typical shapes of writing implements that are different from each other are initially registered as data in the writing input device  1  so that a user can select one of the typical shapes. If the user selects one of the typical shapes appropriate for a writing implement that is to be used for recording information on the recording surface  38 , an area of an imaging device including pixels that output signals generated by photoelectric conversion is changed depending on a selected shape. Accordingly, a load on the writing input device  1  to create image data is reduced. 
       FIG. 13  is a flowchart describing steps performed by the writing input device  1  according to the third embodiment of the present invention. Data regarding shapes of outlines of typical writing implements should be initially stored in the ROM  24  or in the flash memory  26 . The user selects a writing-implement selecting mode by use of a selection key provided in the operation unit  27 . At a step S 301 , the CPU  23  checks whether an operation mode has become the writing-implement selecting mode. If the operation mode has become the writing-implement selecting mode, the CPU  23  displays icons corresponding to the typical writing implements on the LCD  8  at a step S 302 .  FIGS. 14A ,  14 B and  14 C show examples of the icons.  FIG. 14A  shows a first icon indicating writing implements such as a ballpoint pen, a pencil and a mechanical pencil whose holding parts are comparatively thin and whose tip is sharp.  FIG. 14B  shows a second icon indicating writing implements such as a stick and a marking pen with a cap on. Additionally,  FIG. 14C  shows a third, icon indicating writing implements such as a finger. A height from the recording surface  38  in the photographing area  37  necessary for deciding shapes of the writing implements such as the pencil and the marking pen corresponding to the first and the second icons is less than that for deciding the writing implements such as the finger corresponding to the third icon while the writing implements corresponding to the first, second and third icons are contacting the recording surface  38 . 
     Therefore, an area on the CMOS image sensors  16  and  21  including pixels that output signals generated by the photoelectric conversion is changed depending to an icon selected by the user. At a step S 303 , the CPU  23  checks whether the first icon or the second icon has been selected-by the user. If it is determined at the step S 303  that the first icon or the second icon has been selected, the image-processing circuits  17  and  22  reduce the number of pixels in the direction perpendicular to the recording surface  38  that output signals generated by the photoelectric conversion at a step S 304 , followed by proceeding to the step S 101  of the first embodiment ( FIG. 8 ). Subsequently, the steps S 101  through S 109  are executed. If it is determined at the step S 303  that the first icon or the second icon has not been selected, the CPU  23  checks whether the third icon has been selected by the user, at a step S 305 . If it is determined at the step S 305  that the third icon has been selected, the image-processing circuits  17  and  22  increase the number of pixels in the direction perpendicular to the recording surface  38  that output signals generated by the photoelectric conversion at a step S 306 , followed by proceeding to the step S 101  of the first embodiment ( FIG. 8 ). Subsequently, the steps S 101  through S 109  are executed. It should be noted that the image-processing circuits  17  and  22  output a signal specifying the area including pixels that output signals generated by photoelectric conversion to the CMOS image sensors  16  and  21  respectively. 
     A description will now be given of a fourth embodiment of the present invention with reference to  FIG. 15 . In the fourth embodiment of the present invention, typical shapes of writing implements that are different from each other are initially registered as data in the writing input device  1  so that a user can select one of the typical shapes. If the user selects one of the typical shapes appropriate for a writing implement that is to be used for recording information on the recording surface  38 , data about a selected shape is used as reference data for deciding whether an object contacting the recording surface  38  is for recording information on the recording surface  38  or not, thereby increasing accuracy of the above-described decision process, as well as reducing the load on the writing input device  1  to create image data. 
       FIG. 15  is a flowchart describing steps performed by the writing input device  1  according to the fourth embodiment of the present invention. Data related to shapes of outlines of typical writing implements should be initially stored in the ROM  24  or in the flash memory  26 , each data corresponding to identification information of an icon. The typical writing implements correspond to the icons described in the third embodiment ( FIG. 14 ). At a step S 401 , the CPU  23  checks whether an operation mode has become the writing-implement selecting mode by a key operation executed by the user. If the operation mode has become the writing-implement selecting mode, the CPU  23  displays the icons corresponding to the typical writing implements on the LCD  8  at a step S 402 . When detecting that one of the icons has been selected at a step S 403 , the CPU  23  stores identification information of a selected icon in the main memory  25 . At a step S 404 , an information-inputting mode starts following the writing-implement selecting mode. At a step S 405 , the image-processing circuits  17  and  22  convert analog image signals outputted respectively from the CMOS image sensors  16  and  21  to digital image signals in order to obtain a frame of image data, and extract an outline of the object from the frame of the image data. After the outline of the object has been extracted, at a step S 406 , the image-processing circuits  17  and  22  decide whether the object is a writing implement based on a shape of the extracted outline by using the data related to shapes of outlines of typical writing implements that has been stored in the ROM  24  or in the flash memory  26 . In other words, the image-processing circuits  17  and  22  compare data related to the shape of the extracted outline with the data related to shapes of outlines of typical writing implements that corresponds to the identification information of the selected icon stored in the main memory  25 . If it is determined at the step S 406  that both of the data are identical, the image-processing circuits  17  and  22  determine the object as a writing implement (step S 103  in  FIG. 8 ). Subsequently, the steps S 104  through S 109  are executed. 
     A description will now be given of a fifth embodiment of the present invention with reference to  FIG. 16 . In a case that there is a pattern similar to a writing implement in images of the writing implement photographed by the left camera unit  2  and the right camera unit  3 , the writing input device might misunderstand the pattern as the writing implement. In the fifth embodiment, the writing implement is photographed to obtain data related to a shape of the writing implement before a user starts recording information by use of the writing implement on the recording surface  38 , and then the data is stored in a memory. The data is used as reference data for deciding whether an object is the writing implement when the object is contacting the recording surface  38 , thereby increasing accuracy of the above-described decision process, as well as reducing the load on the writing input device  1  to create image data. 
       FIG. 16  is a flowchart describing steps performed by the writing input device  1  according to the fifth embodiment of the present invention. Before the information-inputting mode, a writing implement is photographed under a condition that the writing implement is contacting the recording surface  38  or is close to the recording surface  38 . Additionally, a shape-memory key provided in the operation unit  27  is pressed down by a user for storing data related to a shape of the writing implement in the main memory  25 . When the CPU  23  detects that the shape-memory key has been pressed down at a step S 501 , the image-processing circuits  17  and  22  convert analog image signals outputted from the CMOS image sensors  16  and  21  to digital image signals in order to obtain a frame of image data of the writing implement, and extract an outline of the writing implement from the obtained frame of the image data at a step S 502 . At a step S 503 , after the outline of the writing implement has been extracted, the CPU  23  stores data related to a shape of the outline in the main memory  25 , the data being used for deciding the shape of the writing implement. Once the shape of the outline is stored in the main memory  25 , an operation mode shifts to the information-inputting mode at a step S 504 . At a step S 505 , the image-processing circuits  17  and  22  convert analog image signals outputted from the CMOS image sensors  16  and  21  to digital image signals in order to obtain a frame of image data of an object, and extract an outline of the object from the obtained frame of the image data. At a step S 506 , after the outline of the object has been extracted, the image-processing circuits  17  and  22  decide whether the object corresponds to the writing implement that was initially photographed, based on the outline of the object by use of the data that is related to the shape of the writing implement and is stored in the main memory  25 . In other words, the image-processing circuits  17  and  22  compare data related to the extracted outline of the object with the data related to the shape of the writing implement. Subsequently, the image-processing circuits  17  and  22  proceed to the step S 103  shown in  FIG. 8 . 
     In the above-described embodiments, the writing input device  1  recognizes only one object for recording information on the recording surface  38 . However, there is a case that more than one object, for example, a pen and a finger are recognized simultaneously as writing implements by an image recognition method of the writing input device  1 . A sixth embodiment provides a solution to the above-described case. To be concrete, when a plurality of objects has been recognized simultaneously as writing implements by the writing input device  1 , the writing input device  1  defines an object that is the closest to the left camera unit  2  and the right camera unit  3  as a writing implement. In the sixth embodiment, a description will be given of a case that there are two objects recognized simultaneously as writing implements. As shown in  FIG. 17 , paper is used as a recorded material, whereon a user writes information by use of a ballpoint pen with his or her right hand, and holds the paper with fingers of his or her left hand. In  FIG. 17 , a contact point A is a contact point of the ballpoint pen and the paper. Contact points B, C, D, E and F are contact points of the fingers and the paper. It should be noted that the user&#39;s right hand is not shown in  FIG. 17  since the right hand is not recognized as a writing implement. 
       FIG. 18  is a flowchart describing steps performed by the writing input device  1  according to the sixth embodiment of the present invention. At the left camera unit  2 , the image-processing circuit  17  converts an analog image signal outputted from the CMOS image sensor  16  to a digital image signal in order to obtain a frame of image data of an object, and then extracts an outline of the object from the frame of image data at a step S 601 . At a step S 602 , the image-processing circuit  17  compares the extracted outline with data related to shapes of writing implements such as a pen and a finger that has been stored in the ROM  24  or in the flash memory  26  in order to decide whether the object consists of a plurality of writing implements. Since the thumb and the index finger of the left hand are behind the middle finger of the left hand as shown in  FIG. 17 , the thumb and the index finger are not recognized as writing implements. Consequently, the other three fingers of the left hand and the ballpoint pen are recognized as writing implements by the image-processing circuit  17 . Meanwhile, the above-described image recognition process is performed at the right camera unit  3 . At the right camera unit  3 , the image-processing circuit  22  converts an analog image signal outputted from the CMOS image sensor  21  to a digital image signal in order to obtain a frame of image data of the object, and then extracts an outline of the object from the frame of image data at the step S 601 . At the step S 602 , the image-processing circuit  22  compares the extracted outline with the data related to shapes of writing implements that has been stored in the ROM  24  or in the flash memory  26  in order to decide whether the object consists of a plurality of writing implements. Since the ring finger and the little finger of the left hand are behind the middle finger of the left hand as shown in  FIG. 17 , the ring finger and the little finger are not recognized as writing implements. Additionally, the thumb and the index finger of the left hand are behind the right hand that is not shown in  FIG. 17 , and thus the thumb and the index finger are not recognized as writing implements. Consequently, the middle finger of the left hand and the ballpoint pen are recognized as writing implements by the image-processing circuit  22 . Accordingly, writing implements that are recognized by both of the image-processing circuits are the middle finger of the left hand and the ballpoint pen. 
     If it is determined by both of the image-processing circuits  17  and  22  at the step S 602  that the object consists of a plurality of the writing implements as described above, the image-processing circuits  17  and  22  decide whether the writing implements are contacting the recording surface at a step S 603  similarly to the step S 104  of the first embodiment. If it is determined at the step S 603  that the writing implements are contacting the recording surface, the image-processing circuits  17  and  22  calculate coordinates of the contact point A of the ballpoint pen and the contact point D of the middle finger from the equations EQ1 through EQ4. In  FIG. 19 , the origin of coordinates is provided as an origin P (0,0) at the top left corner of the recording surface. Additionally, a point Q (Xmax, 0) is given at the top right corner of the recording surface. A distance L 1  is a distance from each of the contact points A and D to the origin P. A distance L 2  is a distance from each of the contact points A and D to the point Q. Assuming the coordinates of the contact point A are (x, y), the distances L 1  and L 2  for the contact point A are obtained by use of the following equations.
 
 L 1=√( x   2   +y   2 )
 
 L 2=√((Xmax-− x ) 2   +y   2 )
 
     Similarly, the distances L 1  and L 2  for the contact point D are obtained. Subsequently, at a step S 604 , the sum of the distances L 1  and L 2  is calculated for each of the contact points A and D. In the sixth embodiment, since the sum for the contact point A is greater than that for the contact point D, the image-processing circuits  17  and  22  define an object contacting the paper at the contact point A, that is, the ballpoint pen as a valid writing implement. At a step S 605 , in the case that the image-processing circuits  17  and  22  recognize a plurality of writing implements contacting the recording surface, the image-processing circuits  17  and  22  obtain coordinates of a contact point where the sum of the distances L 1  and L 2  is the smallest, as valid coordinate data, The steps S 108  and S 109  are executed after the step S 605 . 
     If it is determined by both of the image-processing circuits  17  and  22  at the step S 602  that the object does not consist of a plurality of writing implements, the image-processing circuits  17  and  22  proceed to a step S 606 , and check whether a single writing implement has been recognized. If not, the image-processing circuits  17  and  22  proceed to the step S 601 . If it is determined at the step S 606  that a single writing implement has been recognized, the image-processing circuits  17  and  22  obtain coordinates of a contact point of the single writing implement. Subsequently, the steps S 108  and S 109  of the first embodiment are executed. 
     If it is determined at the step S 603  that a plurality of writing implements are not contacting the recording surface at a step S 603 , the image-processing circuits  17  and  22  proceed to the step S 608 , and check whether a single writing implement is contacting the recording surface. If not, the image-processing circuits  17  and  22  proceed to the step S 601 . If it is determined at the step S 608  that a single writing implement is contacting the recording surface, the image-processing circuits  17  and  22  obtain coordinates of a contact point of the single writing implement. Subsequently, the steps S 108  and S 109  of the first embodiment are executed. 
     In  FIG. 19 , an area near a line connecting the origin P and the point Q includes an area that cannot be detected as a recording area of the writing input device  1 . However, such a problem can be solved by changing specifications of the writing input device  1 . For instance, the origin P and the point Q may be provided at locations that are certain distance away in a Y-direction from the writing input device instead of locations contacting the writing input device  1 . 
     According to the sixth embodiment, in a case that a plurality of writing implements such as a pen and a finger is recognized by camera units, an object that is the closest to the camera units is selected as the only writing implement. For example, while a user is writing information on a recording sheet with a pen as well as holding the recording sheet by his or her hand, written data of the pen is recorded in a recording medium as electric data if the pen is placed closer than fingers to the camera units. Additionally, the writing input device  1  according to the sixth embodiment can prevent a user from inputting undesired information to the writing input device  1  in a case that an object other than writing implements is recognized as a writing implement by mistake. 
     A seventh embodiment of the present invention enables simple management of data inputted by a writing implement by defining a size of a recording area as a standard paper size.  FIG. 20  is a flowchart describing steps performed by the writing input device according to the seventh embodiment of the present invention. A length of the recording area  13  in the vertical direction shown in  FIG. 4  is defined, for instance, as a height of a letter size (A4). Such information is initially recorded in the ROM  24 . At a step S 701 , coordinates of a contact point of a writing implement contacting the recording surface are obtained by use of one of the methods described in the first through fifth embodiments. If the obtained coordinates of the contact point are in the defined recording area at a step S 702 , the CPU  23  processes data related to the obtained coordinates as valid data at a step S 703 . To be concrete, the CPU  23  creates depiction data based on a series of coordinate data of the contact point. Subsequently, the CPU  23  displays the depiction data on the LCD  8  through the LCD display-control unit  28  and stores the series of the coordinate data of the contact point in the flash memory  26 . On the other hand, if the obtained coordinates of the contact point are located outside the defined recording area at the step S 702 , the CPU  23  defines the data related to the obtained coordinates as invalid data, and does not execute the above-described displaying and storing processes at a step S 704 . 
     In an eighth embodiment of the present invention, a user can set a size of the recording area  13  to one of a letter size (A4) with a longer side placed in the vertical direction (an A4 height), the letter size with a shorter side placed in the vertical direction (an A4 width), a legal size (B4) with a longer side placed in the vertical direction (a B4 height), the legal size with a shorter side placed in the vertical direction (a B4 width), and the like. Such information is initially stored in the ROM  24 . Additionally, width of the recording area  13  can be altered as a distance changes between the left camera unit  2  and the right camera unit  3  in the eighth embodiment. The expansion/contraction units  6  and  7  shown in  FIG. 2  can expand and contact by a hand operation. By use of the expansion/contraction units  6  and  7 , a user can set the width of the recording area  13  to any of the A4 height, the A4 width, the B4 height and the B4 width. When both of the expansion/contraction units  6  and  7  contract the most, the distance between the left camera unit  2  and the right camera unit  3  becomes the shortest. Consequently, a size of the recording area  13  is set to the A4 height. When both of the expansion/contraction units  6  and  7  expand the most, the distance between the left camera unit  2  and the right camera unit  3  becomes the longest. Consequently, a size of the recording area  13  is set to the B4 width. Additionally, when the expansion/contraction unit  6  on the left contracts the most, and the expansion/contraction unit  7  on the right expands the most, a size of the recording area  13  is set to the B4 height. Additionally, when the expansion/contraction unit  6  on the left expands the most, and the expansion/contraction unit  7  on the right contracts the most, a size of the recording area  13  is set to the A4 width. Each of the expansion/contraction units  6  and  7  is provided with a switch that is not shown in the figures, and thus a state of expansion/contraction of each of the expansion/contraction units  6  and  7  can be detected by checking the switch. In other words, by checking a combination of on/off settings of switches provided in the expansion/contraction units  6  and  7 , the CPU  23  can detect which paper size is selected by a user. 
       FIG. 21  is a flowchart describing steps performed by the writing input device according to the eighth embodiment of the present invention. At a step S 801 , the CPU  23  checks a state of expansion/contraction of each of the expansion/contraction units  6  and  7 . Subsequently, the CPU  23  selects a size of the recording area  13  corresponding to the state of expansion/contraction of each of the expansion/contraction units  6  and  7  from the above-described four sizes at a step S 802 . For instance, when both of the expansion/contraction units  6  and  7  have contracted the most, the CPU  23  sets a size of the recording area  13  to the A4 height. At a step S 803 , the image-processing circuits  17  and  22  obtain coordinates of a contact point of a writing implement contacting the recording surface by performing the steps described in one of the first through fifth embodiments. If the obtained coordinates of the contact point are in the selected recording area at a step S 804 , the CPU  23  processes data related to the obtained coordinates as valid data at a step S 805  similarly to the step S 703  shown in  FIG. 20 . On the other hand, if the obtained coordinates of the contact point are located outside the selected recording area at the step S 804 , the CPU  23  defines the data related to the obtained coordinates as invalid data, and does not process the data at a step S 806 . It should be noted that four types of the states of expansion/contraction are provided in the writing input device  1  for setting the size of the recording area  13 . However, the number of the states can be increased so that there can be more selections for selecting the size of the recording area  13 . 
     According to the eighth embodiment, since a desired recording area can be selected from a plurality of recording areas whose shapes and sizes are different from each other, operability of the writing input device  1  increases. 
     A description will now be given of a ninth embodiment of the present invention with reference to  FIG. 22 . According to the ninth embodiment, before recording information in the recording area  13 , a user can set a size of the recording area  13  freely in a range where coordinates of a writing implement can be obtained in addition to predetermined sizes of the recording area  13 . In other words, the user can set an area larger than the predetermined sizes of the recording area  13  as the recording area  13 . 
       FIG. 22  is a flowchart describing steps performed by the writing input device according to the ninth embodiment of the present invention. When a recording-area setting mode is set at a step S 901  by a user operating keys provided in the operation unit  27 , the image-processing circuits  17  and  22  process a track of coordinates of a contact point of a writing implement on the recording surface as information used for setting the size of the recording area  13  instead of processing the track as data related to an outline of the writing implement, at a step S 902 . In the recording-area setting mode, the image-processing circuits  17  and  22  decide whether the track of the coordinates of the contact point forms a closed area. The closed area may be an area whose outline is formed by only the track of the coordinates of the contact point. Alternatively, the closed area may be an area whose outline is formed by a straight line PQ connecting the origin P and the point Q shown in  FIG. 19  and the track of the coordinates of the contact point. Furthermore, the closed area may be an area whose outline is formed by straight lines PQ, PR and QS shown in  FIG. 23  and the track of the coordinates of the contact point. It should be noted that the straight line PR is drawn perpendicularly to the straight line PQ from the origin P. The straight line QS is drawn perpendicularly to the straight line PQ from the point Q. When a user presses down a confirmation key provided in the operation unit  27  at a step S 903  after specifying an area by moving the writing implement on the recording surface, the image-processing circuits  17  and  22  define the area as the recording area  13  at a step S 904 . 
     For instance at the step S 901 , by use of the operation unit  27  and a guidance displayed on the LCD  8 , a user sets one of recording-area setting modes wherein the straight lines PQ, PR and QS are fixed so that a user can specify only one side RS of a rectangle PQSR as shown in  FIG. 23 . Subsequently, when a user has pressed down a confirmation key provided in the operation unit  27  at the step S 903  after drawing the side RS by use of the writing implement, the image-processing circuits  17  and  22  define the rectangle PQSR as the recording area  13  at the step S 904 , and store coordinates of each of the points P, Q, Rand S as recording-area information in the main memory  25 . 
     After the recording area has been defined at the step S 904 , the recording-area setting mode is cancelled, and the information-inputting mode is set at a step S 905 . Steps S 906  through S 909  correspond to the steps S 701  through S 704  respectively. 
     If it is determined that the confirmation key has not been pressed at the step S 903 , the image-processing circuits  17  and  22  proceed to the step S 902 . If the recording area  13  could not been formed at the step S 904 , the CPU  23  displays a message on the LCD  8  at a step S 910  to notify a user about failure of the formation of the recording area  13 , and proceeds to the step S 902 . 
     In the above-described ninth embodiment, the recording area  13  is the rectangle PQSR. However, the writing input device  1  can manage information about the recording area  13  even if the shape of the recording area  13  is a shape other than a rectangle. 
     According to a tenth embodiment, when the writing input device  1  detects that a user has written information outside the recording area  13 , the writing input device  1  notifies a user that an invalid writing operation has executed by sounding an alarm.  FIG. 24  is a flowchart describing steps performed by the writing input device according to the tenth embodiment of the present invention. At a step S 1001 , the image-processing circuits  17  and  22  obtain coordinates of a contact point of an object that has been recognized as a writing implement in the seventh, eighth and ninth embodiments. Subsequently, at a step S 1002 , the image-processing circuits  17  and  22  determine whether the contact point of the writing implement is in the recording area  13 . If it is determined at the step S 1002  that the contact point is in the recording area  13 , the writing input device  1  processes data related to the obtained coordinates as valid data at a step S 1003 . If it is determined at the step S 1002  that the contact point is located outside the recording area  13 , the writing input device  1  does not process coordinate data of the contact point at a step S 1004 . Additionally, at a step S 1005 , the writing input device  1  outputs an alarm signal from the sound source  30  to the speaker  32  wherefrom an alarming sound is outputted. According to the tenth embodiment, a user can easily identify the recording area  13  even in a case that a recording sheet such as paper is not used as the recording area  13 . In other words, even in a case that the recording area  13  is hardly determined because of a recording surface being a desk or a wall, a user can write information in the recording area  13  smoothly and correctly. 
     In an eleventh embodiment, a frame is provided on the edge of the recording area  13  so that a user can easily notice a range of the recording area  13 . Additionally, from an image photographed by the left camera unit  2  and the right camera unit  3 , the image-processing circuits  17  and  22  do not detect a contact point of a writing implement on a recorded material such as paper in an area outside the recording area  13  where the contact point is behind the frame, thereby reducing the load on the writing input device  1  to execute image processes. 
     In a case that the image-processing circuits  17  and  22  extract an outline of an object from an image photographed by the left camera unit  2  and the right camera unit  3 , a larger contrast of the object and its surrounding area produces a higher accuracy in extracting the outline of the object. In other words, a larger difference in luminance of the object and its surrounding area produces a higher accuracy in extracting the outline of the object. If a writing implement is specified, a background color of the image photographed by the left camera unit  2  and the right camera unit  3  can be set to a color which is the most appropriate to a color of the writing implement. However, if the color of the writing implement is not specified, the background color of the image should be set to a color by which objects with various colors can be easily extracted from the image. For instance, it is assumed that a finger is used as a writing implement. In such case, when the finger is photographed under a regular room light, luminance of the finger is closer to luminance of a white subject than to that of a black subject having the lowest luminance. Accordingly, in the eleventh embodiment, a color of the inner surface of the frame provided on the edge of the recording area  13  is set to black, thereby increasing accuracy in recognizing a shape of an unspecified writing implement and detecting coordinates of a contact point of the unspecified writing implement on a recorded material. 
     In a case that a sheet of paper and the like are not used as the recording area  13 , a frame is provided on the edge of the recording area  13  so that a user can easily distinguish the recording area  13 . As shown in  FIG. 25 , a frame made of a plastic and the like includes three bars  43 ,  44  and  45 . The three bars  43 ,  44  and  45  can be combined or separated by use of combination units  49  and  50 . Shapes of the combination units  49  and  50  are existing shapes. A height of the frame from the recording surface should be set high enough not to be able to recognize a state in which an object recognized as a writing implement is contacting the recording surface outside the recording area  13 . By providing such a frame on the edge of the recording area  13 , a recognition process of a contact point of the object on the recording surface outside the recording area  13  cannot be executed, thereby sharply reducing an amount of processes performed by the writing input device  1 . Additionally, by setting a color of inner surfaces  46 ,  47  and  48  of the above-described bars  43 ,  44  and  45  to black, and further by using materials having low light-reflectance as materials used for creating the bars  43 ,  44  and  45 , accuracy in recognizing a shape of an unspecified writing implement and detecting coordinates of a contact point of the unspecified writing implement on the recording surface is increased. 
     A description will now be given of a twelfth embodiment of the present invention. An amount of electric charge stored in each pixel on a CMOS image sensor in a unit time by photoelectric conversion depends on an amount of light irradiated onto an imaging device. In other words, the amount of electric charge stored in each pixel by the photoelectric conversion in a unit time increases as an amount of incident light to the imaging device increases, and thus a frame rate outputted as image signals can be increased. In addition, a user writes information on a recorded material occasionally in a place where a lighting environment is insufficient. Accordingly, in the twelfth embodiment, accuracy in recognizing a shape of a writing implement and detecting a contact point of the writing implement on the recorded material is increased by irradiating light against the recording area  13  located on the recorded material. When the writing input device  1  is powered on, the LED  9 , the LED  10 , the LED  11 , and the LED  12  are supplied with electric current, and turned on. Consequently, the amount of incident light irradiated to the CMOS image sensors  16  and  21  increases. Thus, the amount of electric charge stored in each pixel by the photoelectric conversion in a unit time increases so that a frame rate outputted as image signals can be increased. 
     Accordingly, accuracy in recognizing a shape of an unspecified writing implement and detecting coordinates of a contact point of the unspecified writing implement on a recording surface can be increased. The twelfth embodiment becomes very effective especially in a case that the writing input device  1  is used in a place where the lighting environment is insufficient. The description has been given of the twelfth embodiment in which each LED is turned on when the writing input device  1  is powered on. Alternatively, each LED in the writing input device  1  may be supplied with a switch, and may be turned on when a switch corresponding the LED is pressed down. 
     In a thirteenth embodiment, in a case that a resolution of reading coordinates is low, by setting an entire reading area (the recording area  13 ) as a part of a page of a data area, written data such as letters inputted by use of a writing implement is combined with a page of written data, and is displayed on an image-display unit, or is stored as a file. Additionally, in a case that a small image-display device that can only display a small number of pixels is used as an image-display device for displaying the written data, the thirteenth embodiment enables displaying images on the image-display device by dividing a page of the data area with a large number of pixels, and writing information in the divided data area. In other words, since a page of the data area is divided into a plurality of blocks, wherein one of the blocks is assigned to a recording area, a page of written data can be created by inputting information in the recording area a number of times even if a resolution of reading information written in the recording area is low. 
     A range of the recording area is limited to an area where a writing implement can be recognized, as shown in  FIG. 4 . However, in the thirteenth embodiment, a description will be given of a case that the recording area is set to a letter (A4) size including the points P, Q, R and S as corners of the recording area as shown in  FIG. 23 . The point P is the origin of coordinates of contact points of a writing implement in the recording area. The point Q is placed at the end of an X-axis drawn from the origin P. A distance between the points P and Q is set to a shorter side (width) of the A4 size by use of the extraction/contraction units  6  and  7  shown in  FIG. 2  by a hand operation. In addition, the distance between the points P and Q is displayed in millimeters on the LCD  8 . If the distance between the points P and Q is equal to a width of a fixed sheet size, the LCD  8  displays letters such as “A4 width” and “B4 width”. Accordingly, a user can check a width of the recording area while writing information in the recording area since a distance between the left camera unit  2  and the right camera unit  3  is displayed in millimeters or by a sheet size on the LCD  8 . 
     A description will now be given of a method of managing written data. The written data is managed by a page having a fixed size. A recording area can be set to any size so that a size of the page can be set to any value. In the thirteenth embodiment, it is assumed that a data size (the number of pixels) of the page is set to an A4 data size (the number of pixels). The number of pixels included in the page is set to an 864-pixel width by an 1140-pixel length based on an ITU-T T.4 related to a document of a group-3 facsimile device. The above-described size of the page is equivalent to 100 dpi (dot per inch) in the width and the length of the page. A page of written data or a plurality of pages of written data may be stored as one file in the flash memory  26 . 
     The description has been given of the method of obtaining coordinates of contact points or writing positions of a writing implement by using the equations EQ1 through EQ4 when units are placed in positions&#39; shown in  FIG. 6 . In the method, the only variable parameter used for obtaining the coordinates is the angle θ shown in the equation EQ1, or the distance “h” between an image-formed location of the optical axis of a wide-angle lens and an image-formed location of a writing position on a CMOS image sensor. 
     In the above-described method, a resolution of reading information written at the writing position depends on a distance measured from the writing position to the left camera unit  2  or to the right camera unit  3 . A concrete description will be given of a relation between the distance and the resolution with reference to  FIG. 26 .  FIG. 26  shows positions of a CMOS image sensor, a wide-angle lens, writing positions (writing points) A, B, C and D. It is assumed that the points A and C are placed on the optical axis of the wide-angle lens for a description purpose. A point E is an image-formed location of the points A and C, and is on a surface of the CMOS image sensor. A point F is an image-formed location positioned at a pixel adjacent to a pixel corresponding to the point E. The points B and D are placed at certain points so that an image of a subject placed at the point B or D can be formed at the point F. It is assumed that angles between lines AB and AE, and between lines CD and CE are 90 degrees. 
     Additionally, a cross section of the line AE and a line BF is named a point G. By setting an angle between lines AG and BG, or between CG and DG as an angle θ, a length of the line AG as a length d 1 , a length of the line CG as a length d 2 , a length of the line AB as a length λ1, and a length of the line CD as a length λ2, the lengths λ1 and λ2 are obtained by the following equations.
 
λ1 =d 1*tan θ  EQ5
 
λ2 =d 2*tan θ  EQ6
 
     It is obvious from the above equations EQ5 and EQ6 that distance ranges λ1 and λ2 of a subject photographed by pixels E and F (pixels where the points E and D are located), which are adjacent to each other on the surface of the CMOS image sensor, vary depending on the distances d 1  and d 2  from the wide-angle lens. The pixels E and F photograph the subject located at the distance d 1  from the point G in the range λ1. On the other hand, the pixels E and F photograph the subject located at the distance d 2  from the point G in the range λ2. This indicates that accuracies in reading coordinates of the writing position are the same in a case of writing information from the point A to the point B, and in a case of writing information from the point C to the point D. 
     A resolution measured in dpi of reading the coordinates of the writing position on the line AB is obtained by dividing one inch that is a unit length by the distance λ1 (inch). In addition, a resolution of reading the coordinates of the writing position on the line CD is obtained by dividing one inch by the distance λ2 (inch). In a case that the number of pixels that can be read by one of the left camera unit  2  and the right camera unit  3  in a horizontal direction of the CMOS image sensors  16  and  21 , that is, a direction parallel to the recording surface  38  in a photographed image shown in  FIG. 9 , is 640 pixels, a resolution of reading coordinates at the points R and S is about 28 dpi in an A4-sized recording area shown in  FIG. 23 . Additionally, a resolution of reading coordinates at the center of the A4-sized recording area is about 56 dpi. As described above, the closer to the left camera unit  2  and the right camera unit  3  the writing position is in the recording area, the more densely the coordinates are read by the CMOS image sensors  16  and  21 . On the contrary, the farther from the left camera unit  2  and the right camera unit  3  the writing position is in the recording area, the more roughly the coordinates are read by the CMOS image sensors  16  and  21 . 
     Now, it is assumed that the LCD  8  can display 432 pixels in the horizontal direction and 285 pixels in the vertical direction. In a case of displaying a page of written data whose size is the 864-pixel width by the 1140-pixel length on the LCD  8 , the page must be divided into several blocks.  FIG. 27  is a block diagram showing an embodiment of a method to divide the page of written data. As shown in  FIG. 27 , the number of pixels included in the page of written data is divided by the number of pixels displayed on the LCD  8  into eight displaying blocks  51 . In other words, the number of pixels in each of the divided displaying blocks  51  is equal to the number of pixels displayed on the LCD  8 . This displaying block  51  (432×285 pixels) is separated into a left block and a right block, each of the left and the right blocks having the size of 216×285 pixels. Subsequently, each of the left and right blocks is named a writing block  52 , and is assigned to the A4-sized recording area shown in  FIG. 23  to fit to the A4 size.  FIG. 28  shows an embodiment in which a page of written data is divided into a plurality of the writing blocks (recording areas)  52 . A size of the writing block  52  is exactly equal to a half of the displaying block  51  so that a page of written data is evenly divided into sixteen blocks.  FIG. 29  shows a relation between a page of written data and the recording area in a case of writing information in a fourth writing block (a fourth recording area) shown in  FIG. 28 . A size of a recording area shown in  FIG. 29  is a letter size (A4). In addition, the recording area is provided with paper whereon a line of letters is written by use of a pen. 
     A description will now be given of processes performed in the thirteenth embodiment in a case of writing information in one of the writing blocks  52  created as described above.  FIG. 30  is a flowchart describing steps performed by the writing input device according to the thirteenth embodiment of the present invention. Steps S 1101  through S 1107  are executed similarly to the steps S 101  through S 107  of the first embodiment shown in  FIG. 8  in order to obtain coordinates (x, y) of a contact point of a writing implement on a recording surface. A unit of the coordinates (x, y) is the same as a unit of the distance L shown in  FIG. 6 , and is millimeters in the thirteenth embodiment. Since the size of the writing block  52  is exactly 1/16 of the size of a page of written data, the coordinates (x, y) of the contact point (writing position) in the recording area are expressed in the numbers of pixels counted from the origin of the page in an X-axis direction and in a Y-axis direction. Initially, assuming a resolution of reading coordinates (an interval of reading coordinates) is even throughout the recording area (the writing block  52 ), coordinates (x_dot, y_dot) expressed in pixels are calculated from the coordinates (x, y) expressed in millimeters in one of the writing blocks  52  by use of the following equations at a step S 1108 .
 
 x _dot= x /(an interval of reading coordinates in the X-axis direction)  EQ7
 
 y _dot= y /(an interval of reading coordinates in the Y-axis direction)  EQ8
 
     Subsequently, by setting the top left corner of a page of written data as the origin of the page, an origin of an “n”th writing block  52  can be expressed as coordinates (x_org(n), y_org(n)). A range of the value “n” is from 0 to 15. At a step S 1109 , coordinates (x_dot_page, y_dot_page) of the writing position in a page of written data are obtained from the following equations.
 
 x _dot_page= x _org( n )+ x _dot  EQ9
 
 y _dot_page= y _org( n )+ y _dot  EQ 10
 
     The writing input device  1  manages the coordinates (x_dot_page, y_dot_page) expressed in pixels as written data. For instance, in a case that information is written at coordinates ( 100 ,  200 ) in a tenth writing block, coordinates ( 100 ,  200 ) in the tenth writing block are converted into coordinates ( 316 ,  770 ) in a page. It should be noted that coordinates of the origin of the tenth writing block are ( 216 ,  570 ). 
     At a step S 1110 , the CPU  23  stores a series of coordinate data of a contact point that has been obtained while the writing implement was contacting the recording surface in one of the writing blocks in a memory as written data of the writing block in a page of written data. In addition, the CPU  23  creates depiction data from the series of the coordinate data by use of a method of connecting each set of coordinates with a straight line, for example, and displays the depiction data on the LCD  8  through the LCD display-control unit  28  at a step S 1111 . 
     It is assumed in the thirteenth embodiment that the resolution of reading coordinates is even throughout the entire recording area when obtaining the coordinates (x_dot, y_dot) expressed in pixels in order to simplify the description. However, in reality, the resolution of reading the coordinates varies depending on a distance from the left camera unit  2  or the right camera unit  3  to the coordinates (x_dot, y_dot). A method of making a pixel density of written data even throughout the entire recording area will be described later in other embodiments. 
     Additionally, the following equations EQ11 and EQ12 can be substituted for the equations EQ7 and EQ8 for obtaining the coordinates (x_dot, y_dot) expressed in pixels from the coordinates (x, y).
 
 x _dot=864×( x/ 215)×(¼)  EQ11
 
 y _dot=1140×( y/ 290)×(¼)  EQ12
 
     The equations EQ11 and EQ12 are derived from the following facts. The numbers of pixels in the width and the length of a page of written data are respectively 864 pixels and 1140 pixels. The width and the length of the page are respectively 215 millimeters and 290 millimeters. In addition, the width and the length of one of the writing blocks corresponding to the recording area are ¼ of the width and the length of the page respectively. 
     In a fourteenth embodiment of the present invention, the recording area is assigned to any area in a page of a data area. Additionally, in a case that the resolution of reading coordinates in the recording area is low, a page of written data is created by writing data in the recording area several times. In other words, in the above-described thirteenth embodiment, the description has been given of the method of dividing the number of pixels in a page of the data area into 8 blocks, displaying one of the blocks on the LCD  8 , and assigning half of a block to the recording area. On the other hand, in the fourteenth embodiment, a description will be given of a method of assigning a pixel-displaying area of the LCD  8  to any area in a page of the data area, and then assigning a part of the pixel-displaying area to the recording area. Similarly to the thirteenth embodiment, the LCD  8  can display 432 pixels in the horizontal direction and 285 pixels in the vertical direction. A location of the pixel-displaying area of the LCD  8  can be moved freely to any location in a page of the data area by a user operation. A method of moving the pixel-displaying area of the LCD  8  will be described later in other embodiments. 
       FIG. 31  is a block diagram showing an embodiment of a pixel-displaying area  53  of the LCD  8  in a page of the data area.  FIG. 31  further includes a displaying area  54  for writing that is a 216 pixel by 285 pixel shaded area located at the center of the pixel-displaying area  53 . In other words, coordinates of the origin (the top left corner) of the pixel-displaying area  53  are (300, 300) in  FIG. 31 . Additionally, coordinates of the origin of the displaying area  54  for writing are (408, 300). In the same manner as the thirteenth embodiment, the coordinates (x, y) of a contact point (a writing position) of a writing implement contacting a recording surface are obtained. Subsequently, the coordinates (x, y) are converted to the coordinates (x_dot, y_dot) expressed in pixels by use of the equations EQ7 and EQ8. Assuming that the top left corner of a page of the data area is the origin, coordinates of the starting point of the recording area, that is, the top left corner of the recording area, expressed in pixels are named coordinates (x_org, y_org). Coordinates (x_dot_page, y_dot_page) of the writing position in a page of the data area are expressed as below.
 
 x _dot_page=x_org+ x _dot  EQ13
 
 y _dot_page=y_org+ y _dot  EQ14
 
     For example, if data is written at coordinates ( 100 ,  200 ) in the displaying area  54  for writing shown in  FIG. 31 , the coordinates ( 100 ,  200 ) in the displaying area  54  for writing are converted to coordinates ( 508 ,  500 ) in a page of the data area. The writing input device  1  manages the coordinates (x_dot_page, y_dot_page) expressed in pixels as written data. 
     As described above, the fourteenth embodiment is characterized by the function to assign the pixel-displaying area  53  to any location in a page of the data area. After a location of the pixel-displaying area  53  has been set in a page of the data area, the steps S 1110  and S 1111  shown  FIG. 30  of the thirteenth embodiment are executed. It should be noted that a displaying area for writing is substituted for a writing block in the step S 1110  in the fourteenth embodiment. According to the fourteenth embodiment, the recording area is assigned to a desired area in a page of the data area so that the writing input device  1  can create and manage a page of written data that includes a large number of pixels by writing data in the recording area a plurality of times even in a case that the resolution of reading coordinates is low in the recording area. Additionally, operability of the writing input device  1  increases when a user writes data in the desired area of a page of the data area. 
     In a fifteenth embodiment, an area corresponding to a recording area is displayed on a displaying unit distinctively so that a user can recognize easily which part of a page of a data area he or she is currently writing data in, thereby improving operability of the writing input device  1 . In the above-described thirteenth embodiment, in a case that a writing block corresponding to the recording area is displayed on a monitor of the LCD  8 , the writing block is displayed in the right or left half of a displaying block as shown in  FIGS. 27 and 28 . On the other hand, in the fourteenth embodiment, a displaying area for writing that corresponds to the recording area is displayed at the center of the monitor of the LCD  8 , as shown in  FIG. 31 . In the fifteenth embodiment, a border of the displaying area for writing is accentuated on the monitor of the LCD  8  in order for a user to easily distinguish the displaying area for writing.  FIG. 32A  shows an embodiment corresponding to the thirteenth embodiment of an emphasized displaying area  55  for writing on the monitor of the LCD  8 .  FIG. 32B  shows an embodiment corresponding to the fourteenth embodiment of an emphasized displaying area  56  for writing on the monitor of the LCD  8 . 
     In a sixteenth embodiment, a description will be given of a method of displaying an area corresponding to a recording area on a displaying unit distinctively so that a user can recognize easily which part of a page of a data area he or she is currently writing data in, thereby improving operability of the writing input device  1 . In the thirteenth embodiment, the size of a writing block is set to exactly 1/16 of the size of a page of the data area as shown in  FIG. 28 . In such case, it is convenient to recognize a location of a writing block corresponding to a current recording area by displaying the location of the writing block with locations of all the writing blocks. Accordingly, a block-location displaying key is provided in the operation unit  27  for displaying the writing block on the LCD  8 . 
       FIG. 33  is a flowchart describing steps performed by the writing input device according to the sixteenth embodiment of the present invention. At a step S 1201 , the writing input device  1  checks whether the block-location displaying key has been pressed. If it is determined at the step S 1201  that the block-location displaying key has been pressed, a situation  57  in which a page is divided into blocks is displayed on the LCD  8 , wherein a location of a writing block  58  is specified. In  FIG. 34 , the location of the writing block  58  (a writing block  10 ) is displayed with its luminance being inverted from other blocks in a page of the data area, at a step S 1202 . If it is determined at a step S 1203  that the block-location displaying key has been pressed again, the LCD  8  displays image data that had been displayed previously before the situation  57  was displayed thereon, for instance, a screen shown in  FIG. 32A  or  FIG. 32B , at a step S 1204 . According to the sixteenth embodiment of the present invention, an area corresponding to the recording area is displayed on the displaying unit distinctively so that a user can recognize easily which part of a page of the data area he or she is currently writing data in, thereby improving operability of the writing input device  1 . 
     A description will now be given of a seventeenth embodiment of the present invention. In the seventeenth embodiment, writing data in any part of a page of a data area is enabled since any of writing blocks corresponding to a recording area can be selected, thereby improving operability of the writing input device  1 .  FIG. 35  is a flowchart describing steps performed by the writing input device according to the seventeenth embodiment of the present invention. In the seventeenth embodiment, a direction-specifying key including up, down, left and right buttons is provided in the operation unit  27 . If it is determined at a step S 1301  that the block-location displaying key has been pressed, a location of the writing block  58  (a writing block  10 ) is displayed on the LCD  8  with its luminance being inverted from other blocks in a page of the data area as shown in  FIG. 34 , at a step S 1302 . Subsequently, if it is determined at a step S 1303  that the direction-specifying key has been pressed, the writing block  58  corresponding to the recording area is moved to a direction specified by use of the direction-specifying key, and is displayed with its luminance being inverted at a step S 1304 . For example, in a case that the writing block  10  shown in  FIG. 34  corresponds to the writing block  58 , a writing block corresponding to the recording area is set to a writing block  11  when the right button of the direction-specifying key is pressed once, and is displayed with its luminance being inverted.  FIG. 36  shows the LCD  8  displaying that a writing block  59  corresponding to the recording area is moved from the writing block  10  to a writing block  11 . Luminance of the writing block  59  before having been moved to the writing block  11  is inverted back to the original value at a step S 1305 . 
     According to the seventeenth embodiment, writing data in any part of a page of the data area is enabled since any of the writing blocks corresponding to the recording area can be selected, thereby improving operability of the writing input device  1 . 
     An eighteenth embodiment enables free movement of an area corresponding to the recording area in a page of a data area, and thus simplifies writing data in any part of a page of the data area, thereby improving operability of the writing input device  1 . The direction-specifying key is used for selecting a writing block in the seventeenth embodiment. On the other hand, the direction-specifying key is used for moving the pixel-displaying area  53  and the displaying area  54  for writing by a pixel in the eighteenth embodiment. The pixel-displaying area  53  of the LCD  8  and the displaying area  54  for writing that corresponds to the recording area in the pixel-displaying area  53  are shown in  FIG. 31 . When the direction-specifying key is pressed, the pixel-displaying area  53  or the displaying area  54  for writing is moved by a fixed number of pixels to a direction specified by use of the direction-specifying key. The operation unit  27  additionally includes a moving-area selecting key used for selecting either the pixel-displaying area  53  or the displaying area  54  for writing as an object of moving. By use of the moving-area selecting key, one of the pixel-displaying area  53  and the displaying area  54  for writing is selected and is moved to the direction specified by use of the direction-specifying key. 
       FIG. 37  is a flowchart describing steps performed by the writing input device according to the eighteenth embodiment of the present invention. A description will initially be given of a case of moving the pixel-displaying area  53  of the LCD  8 . The LCD  8  can display an image having a size of a 432-pixel width by a 285-pixel length at most. A user initially selects one of the pixel-displaying area  53  and the displaying area  54  for writing by use of the moving-area selecting key, followed by pressing the direction-specifying key to move the selected area. The writing input device  1  checks whether the moving-area selecting key has been pressed at a step S 1401 . If the writing input device  1  determines at the step S 1401  that the moving-area selecting key has been pressed, the writing input device  1  proceeds to a step S 1402 , and checks whether a selected area is the pixel-displaying area  53  of the LCD  8 . If it is determined at the step S 1402  that the pixel-displaying area  53  has been selected, the writing input device  1  further checks whether the direction-specifying key has been pressed at a step S 1403 . If it is determined at the step S 1403  that the direction-specifying key has been pressed, a desired area (the pixel-displaying area  53 ) in a page of the data area is displayed on the LCD  8  after being moved in a direction specified by use of the direction-specifying key, at a step S 1404 . 
       FIG. 38  is a diagram showing an embodiment of a pixel-displaying area  60  displayed on the LCD  8 . In  FIG. 38 , a displaying area  61  for writing that corresponds to the recording area is displayed at the center of the pixel-displaying area  60 . The pixel-displaying area  60  displayed on the LCD  8  additionally includes a summarized-location displaying area  62  at a top right corner thereof in which a location of the pixel-displaying area  60  in a page of the data area is displayed. The summarized-location displaying area  62  takes a format of a reduced image of a diagram shown in  FIG. 34 , for example. The pixel-displaying area  60  shown in  FIG. 38  further includes a series of letters already written on in the upper area thereof. 
     A description will now be given of a case of moving the displaying area  61  for writing in the pixel-displaying area  60 . It should be noted that the pixel-displaying area  53  corresponds to the pixel-displaying area  60 . In addition, the displaying area  54  for writing corresponds to the displaying area  61  for writing. The writing input device  1  initially checks whether the moving-area selecting key has been pressed at the step S 1401  of  FIG. 37 . If the writing input device  1  determines at the step S 1401  that the moving-area selecting key has been pressed, the writing input device  1  proceeds to the step S 1402 , and checks whether a selected area is the pixel-displaying area  60  of the LCD  8 . If it is determined at the step S 1402  that the displaying area  61  for writing has been selected instead of the pixel-displaying area  60 , the writing input device  1  further checks whether one of the up, down, left and right buttons of the direction-specifying key has been pressed at a step S 1405 . If it is determined at the step S 1405  that the one of the buttons has been pressed, at a step S 1406 , the writing input device  1  moves a frame on the LCD  8  indicating the displaying area  61  for writing by 30 pixels to a direction specified by use of the direction-specifying key, and again displays the displaying area  61  for writing at a new location. In a case that an instruction to move the displaying area  61  for writing to the right (left) has been inputted when the number of pixels remaining on the right (left) side of the displaying area  61  in the pixel-displaying area  60  is less than 30 pixels, the displaying area  61  is moved by the number of pixels remaining.  FIG. 39  is a diagram showing the displaying area  61  for writing that has been moved to the left edge of the pixel-displaying area  60  from the position shown in  FIG. 38  by the left button of the direction-specifying key being pressed for four times. 
     According to the eighteenth embodiment, an area corresponding to the recording area can be moved freely in a page of the data area, thereby improving operability of the writing input device  1 . 
     A description will now be given of a nineteenth embodiment of the present invention. In a case of using a lens for the left camera unit  2  and the right camera unit  3 , a larger distance from one of the left camera unit  2  and the right camera unit  3  produces a lower resolution of reading coordinates. Thus, the nineteenth embodiment provides a method of preventing deterioration of an image caused by lack of written data by executing an interpolation process against the written data in an area where the resolution of reading coordinates is low. Additionally, the nineteenth embodiment provides a method of making pixel density and image quality of written data obtained by a writing implement moving a certain distance substantially even throughout the entire recording area, by executing an interpolation process or a decimation process properly based on a resolution of reading coordinates at a writing position of the writing implement. 
     In the nineteenth embodiment, the writing input device  1  manages a page of written data in the number of pixels corresponding to 100 dpi, that is, the 864-pixel width by the 1140-pixel length. Since the size of the recording area corresponds to 1/16 of the size of a page of the written data as shown in  FIG. 28 , coordinates of the writing position are desirably read at 25 dpi in the recording area. 
     In a case that the number of pixels read by a CMOS image sensor provided in each camera unit in the horizontal direction (a direction parallel to a recording surface of an image photographed by each camera unit) is 640 pixels, the resolution of reading coordinates at the points R and S in the A4-sized recording area shown in  FIG. 23  is about 28 dpi. Additionally, the resolution of reading coordinates at the center of the recording area is about 56 dpi. In other words, the closer to the left camera unit  2  and the right camera unit  3  the writing position is, the more densely coordinates of the writing position are read by the CMOS image sensors  16  and  21 . On the contrary, the farther from the left camera unit  2  and the right camera unit  3  the writing position is, the more roughly the coordinates of the writing position are read by the CMOS image sensors  16  and  21 . However, a resolution of reading coordinates throughout the entire recording area only needs to be higher than 25 dpi. Thus, the decimation process is executed on the written data, that is, a series of coordinates of the writing position, throughout the entire recording area. The closer to the left camera unit  2  and the right camera unit  3  the writing position of the writing implement is, the higher the resolution of reading coordinates is. Thus, the closer to the left camera unit  2  and the right camera unit  3  the writing position is, the higher a rate of decimation should be. On the other hand, the farther from the left camera unit  2  and the right camera unit  3  the writing position is, the lower the resolution of reading coordinates is. Thus, the farther from the left camera unit  2  and the right camera unit  3  the writing position is, the lower the rate of decimation should be. Written data whose size is adapted to 1/16 of the size of a page (216 pixels by 285 pixels) is obtained because of the above-described execution of the decimation processes. 
     A description will now be given of a method of calculating a resolution of reading coordinates in the recording area.  FIG. 40  is a diagram used for describing a method of calculating the resolution of reading coordinates at a point T in the recording area.  FIG. 40  shows the left camera unit  2 , the right camera unit  3 , the mirror  14  and the mirror  19 . An image of a writing implement located at the point T is obtained by light reflected at around the center of the mirrors  14  and  19 . However, it is assumed that the centers of the wide-angle lenses  15  and  20  are located respectively at points P and Q that are corners of the recording area for the purpose of simplifying the description. Coordinates of the points P and Q are respectively (0, 0) and (215, 0) since a line PQ is a width of an A4-sized recording area. 
     A point T 1  is provided in the recording area so that image-formed locations of the points T and T 1  are at pixels adjacent to each other on the CMOS image sensor  16  of the left camera unit  2 . Similarly, a point T 2  is provided in the recording area so that image-formed locations of the points T and T 2  are at pixels adjacent to each other in the CMOS image sensor  21  of the right camera unit  3 . An angle θ corresponds, to a photographing range of each pixel on the CMOS image sensors  16  and  21 , and depends on a view angle of each of the left camera unit  2  and the right camera unit  3 . Lengths of lines PT, QT, TT 1  and TT 2  are named k 1 , k 2 , L 1  and L 2  respectively. An angle formed by lines PT 1  and TT 1 , and an angle formed by lines QT 2  and TT 2  are set to 90 degrees. In addition, coordinates of the point T are set to (x, y). Accordingly, values of lengths k 1  and k 2  are obtained as follows.
 
 k 1=√( x   2   +y   2 )  EQ15
 
 k 2=√((215 −x ) 2   +y   2 )  EQ16
 
     Subsequently, values of lengths L 1  and L 2  can be obtained from the following equations.
 
 L 1 =k 1*sin θ  EQ17
 
 L 2 =k 2*sin θ  EQ18
 
     The coordinates (x, y) of the point T obtained from the equations EQ1 through EQ4 are expressed in millimeters so that the lengths L 1  and L 2  obtained from the equations EQ17 and EQ18 are expressed also in millimeters. Thus, a unit of the lengths L 1  and L 2  should be converted from a millimeter to an inch by use of a fact that one-millimeter is equal to about 0.03937 inch. Subsequently, a resolution Rdiv_L of reading coordinates by the left camera unit  2  and a resolution Rdiv_R of reading coordinates by the right camera unit  3  at the point T are obtained respectively by dividing one inch by the length L 1  expressed in inches and by the length  2  expressed in inches.
 
Rdiv —   L= 1/( L 1×0.03937)  EQ19
 
Rdiv —   R= 1/( L 2×0.03937)  EQ20
 
     Since the point T is provided in the recording area so that the value of k 1  is greater than the value of k 2  as shown in  FIG. 40 , the value of L 1  obtained from the equation EQ17 is greater than the value of L 2  obtained from the equation EQ18. Thus, the value of the resolution Rdiv_R obtained from the equation EQ20 is greater than the value of the resolution Rdiv_L obtained from the equation EQ19.
 
Rdiv —   R &gt;Rdiv —   L   EQ21
 
     As seen in the equation EQ21, the resolution of reading coordinates by the right camera unit  3  is higher than the resolution of reading coordinates by the left camera unit  2 . 
     As described above, the resolution of reading coordinates by the left camera unit  2  is different from the resolution of reading coordinates by the right camera unit  3  at any point except a point where the values of k 1  and k 2  are identical. Accordingly, the writing input device  1  calculates a vector between each coordinate data belonging to a series of the coordinate data, and decides to use one of resolutions of reading coordinates by the left camera unit  2  and by the right camera unit  3  based on a direction of the vector between each set of coordinates, for executing the decimation process on written data. For example, the resolution of reading coordinates by the left camera unit  2  is used when a user is writing data in a top-right direction as shown in  FIG. 41A . On the other hand, the resolution of reading coordinates by the right camera unit  3  is used when the user is writing data in a bottom-right direction. Similarly, the resolution of reading coordinates by the right camera unit  3  is used when the user is writing data in a top-left direction. The resolution of reading coordinates by the left camera unit  2  is used when the user is writing data in a bottom-left direction. 
       FIG. 42  is a flowchart describing steps performed by the writing input device according to the eighteenth embodiment of the present invention. The writing input device  1  initially checks whether coordinates have been inputted to the recording area at a step S 1501 . If it is determined at the step S 1501  that the coordinates have been inputted to the recording area, the writing input device  1  inspects a direction of taking in coordinate data at a step S 1502 . If the direction of taking in coordinate data is the top-right or bottom-left direction, the writing input device  1  obtains the resolution of reading coordinates by the left camera unit  2  at a step S 1503 . If the direction of taking in coordinate data is the bottom-right or top-left direction, the writing input device  1  obtains the resolution of reading coordinate data by the right camera unit  3  at a step S 1506 . At a step S 1504  following the steps S 1503  and S 1506 , the writing input device  1  executes the decimation process on written data inputted thereto at a fixed rate of decimation that corresponds to the resolution of reading coordinates by a camera unit selected at the step S 1502  so that a pixel density of the written data becomes 100 dpi. Subsequently, at a step S 1505 , the writing input device  1  adds the written data that has been decimated at the step S 1504  to a recording area that corresponds to the written data in a page of written data as shown in  FIG. 29 . In a case that there is a data-storing operation, the writing input device  1  stores a renewed page as a file in the flash memory  26 . It should be noted that a resolution of reading coordinates during a data-writing process in the recording area varies according to coordinates of the writing position. Accordingly, the entire recording area may be equally divided into a plurality of areas, wherein a resolution of reading coordinates in each area may be set to a single value, for example, a value at the center of the area. 
     A description will now be given of a method of executing an interpolation process on written data. The above-described processes shown in  FIG. 42  may be applied to an interpolation process instead of a decimation process. In such case, the writing input device  1  obtains a vector between each set of coordinates of written data, and decides which of the left camera unit  2  or the right camera unit  3  is to be used for calculating a resolution of reading coordinates. In this method of executing an interpolation process on written data, the writing input device  1  manages a page of written data in a size of a 1728-pixel width by a 2280-pixel length, which corresponds to 200 dpi. Since the size of the recording area is 1/16 of a page of the written data, the writing input device  1  needs to read coordinates of a writing position at 50 dpi that is ¼ of the resolution of a page of the written data. However, in a case that the number of pixels read by the CMOS image sensors  16  or  21  in the horizontal direction is 640 pixels, the resolution of reading coordinates at the points R and S in the A4-sized recording area shown in  FIG. 23  is about 28 dpi so that the CMOS image sensors  16  and  21  cannot read the coordinates of the points Rand S at 50 dpi. 
     Accordingly, the writing input device  1  generates written data at 50 dpi by executing the interpolation process on written data, that is, a series of coordinates read by the CMOS image sensors  16  and  21 , in a case that the resolution of reading coordinates is lower than 50 dpi. A spline-curve method and a Bezier-curve method are used in the interpolation process executed on the written data. The spline-curve method is a method of interpolating coordinates at a fixed interval on a curve after obtaining the curve that includes all the coordinates obtained by the CMOS image sensors  16  and  21  thereon. The Bezier-curve method is a method of interpolating coordinates at a fixed interval on a curve after obtaining the curve that includes first and last coordinates provided in a series of coordinates of a writing position thereon by using coordinates located between the first and last coordinates only for deciding a shape of the curve. In other words, the first and last coordinates are on a Bezier curve. However, other coordinates located between the first and last coordinates are not necessarily on the Bezier curve. As described above, the writing input device  1  executes the interpolation process on written data in a case that a resolution of reading coordinates is less than 50 dpi according to the writing position. Alternatively, the writing input device  1  executes the decimation process on written data in a case that a resolution of reading coordinates is higher than 50 dpi. Subsequently, the writing input device  1  adds the written data having its pixel density being 200 dpi to a recording area corresponding to the written data in a page of written data. 
     A description will now be given of a twentieth embodiment of the present invention. The twentieth embodiment provides a method of implementing the present invention by use of software.  FIG. 43  is a block diagram showing a system wherein the present invention is implemented by use of software. The system shown in  FIG. 43  includes a coordinate-inputting unit  70 , a CPU  71 , a memory  72 , an image-displaying device  73 , a CD-ROM device  74 , a CD-ROM  75 , and a communication device  76 . The coordinate-inputting unit  70  includes the left camera unit  2  and the right camera unit  3  shown in  FIG. 3 . The CPU  71  executes the steps and functions that have been described in each of the previous embodiments on an image photographed by the left camera unit  2  and the right camera unit  3 . Subsequently, the CPU  71  displays depiction data on the image-displaying device  73 , and stores written data in the memory  72 . A program executing the above-described processes is stored in a recording medium such as the CD-ROM  75 . The program stored in the recording medium is read by the CD-ROM device  74 , and is installed in the system, thereby executing the functions described in the above-described embodiments. The program may be supplied to the system by being downloaded from a server and the like through the communication device  76  and a network  77 . 
     As described above, the present invention enables use of a desired writing implement and a desired recorded material whose recording surface is a plane for a writing input device. Additionally, according to the present invention, the writing input device can record data in a recording medium in real time while the data is being written by use of a writing implement on the recording surface. Additionally, the writing input device can create and manage a page of written data by dividing the page into a plurality of areas, and then by assigning each of the areas to a recording area even in a case that a resolution of reading coordinates is low in the recording area. Additionally, the writing input device can control a pixel density of the written data to be even throughout the entire recording area. Furthermore, the writing input device can control displaying the recording area on a LCD for improving operability of writing data in the recording area. 
     The above description is provided in order to enable any person skilled in the art to make and use the invention and sets forth the best mode contemplated by the inventors of carrying out the invention. 
     The present invention is not limited to the specially disclosed embodiments and variations, and modifications may be made without departing from the scope and spirit of the invention. 
     The present application is based on Japanese Priority Application No. 11-369699, filed on Dec. 27, 1999, the entire contents of which are hereby incorporated by reference.