Patent Publication Number: US-8994761-B2

Title: Information display control apparatus, information display control method, and storage medium storing information display control program

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2011-140938, filed Jun. 24, 2011, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an information display apparatus, information display control method, and a storage medium storing program, suitable for a foldable electronic organizer, electronic book, or the like. 
     2. Description of the Related Art 
     Studies have been conducted on techniques of improving display quality by adjusting the viewing angle of a liquid crystal in one display panel by detecting its tilt angle. 
     The conventional technique is effective only for one display panel. In contrast to this, there are many types of foldable apparatuses using two display panels, such as currently available electronic dictionary apparatuses, cellular phone terminals, and portable video game machines. When using an apparatus having two display panels, the line of sight of the user differs with respect to these display panels. For this reason, even if one display panel is properly adjusted, the other display panel is not properly adjusted because of the difference in line-of-sight, angle between the two display panels, resulting in deterioration in display quality. That is, the technique disclosed in above patent literature cannot be applied to such an apparatus. 
     Under the circumstance, it is desired to provide an information display apparatus with a plurality of display panels, capable of ensuring optimal visual fields regardless of the angles at which the user sees the respective display panels and a program. 
     BRIEF SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided an information display apparatus comprising: a plurality of display units separately arranged in a foldable housing; a detection unit configured to detect posture angles of the plurality of display units; a gamma storage unit configured to store gamma correction values for the plurality of display units according to a relationship between the posture angles; and a display control unit configured to perform gamma correction on the plurality of display units by referring to the gamma storage unit based on the posture angles of the plurality of display units which are detected by the detection unit. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a front view showing the outer arrangement of an electronic dictionary apparatus according to the first embodiment of the present invention; 
         FIG. 2  is a block diagram showing the functional arrangement of an electronic circuit according to the first embodiment; 
         FIG. 3  is a block diagram showing another functional arrangement of the electronic circuit according to the first embodiment; 
         FIG. 4A  is a view showing two basic forms when the user uses an electronic dictionary apparatus according to the first embodiment while holding it; 
         FIG. 4B  is a view showing the two basic forms when the user uses the electronic dictionary apparatus according to the first embodiment while holding it; 
         FIG. 5  is a flowchart showing the contents of display correction processing in accordance with the angles of both the main and auxiliary screens according to the first embodiment; 
         FIG. 6A  is a view exemplifying the contents of a gamma correction value table stored in a program memory according to the first embodiment; 
         FIG. 6B  is a view exemplifying the contents of a gamma correction value table stored in the program memory according to the first embodiment; 
         FIG. 6C  is a view exemplifying the contents of a gamma correction value table stored in the program memory according to the first embodiment; 
         FIG. 7A  is a view showing the positional relationship between an eye of the user and each screen at the time of use of an electronic dictionary apparatus according to the first embodiment placed in the stationary position; 
         FIG. 7B  is a view showing the positional relationship between the eye of the user and each screen at the time of use of the electronic dictionary apparatus according to the first embodiment held in the stationary position; 
         FIG. 8A  is a view showing the positional relationship between the eye of the user and each screen at the time of use of the electronic dictionary apparatus according to the first embodiment held in the portrait position; 
         FIG. 8B  is a view showing the positional relationship between the eye of the user and each screen at the time of use of the electronic dictionary apparatus according to the first embodiment held in the portrait position; 
         FIG. 9A  is a view showing the positional relationship between the eye of the user and each screen at the time of use of the electronic dictionary apparatus according to the first embodiment held in the landscape position; 
         FIG. 9B  is a view showing the positional relationship between the eye of the user and each screen at the time of use of the electronic dictionary apparatus according to the first embodiment held in the landscape position; 
         FIG. 10  is a flowchart showing the contents of display correction processing to be performed in accordance with the angles of both the main and auxiliary screens according to the second embodiment of the present invention; 
         FIG. 11A  is a view exemplifying the contents of a gamma correction value table stored in a program memory according to the second embodiment; 
         FIG. 11B  is a view exemplifying the contents of a gamma correction value table stored in the program memory according to the second embodiment; 
         FIG. 11C  is a view exemplifying the contents of a gamma correction value table stored in the program memory according to the second embodiment; 
         FIG. 12A  is a view showing the positional relationship between the eye of the user and each screen at the time of use of an electronic dictionary apparatus according to the second embodiment held in the portrait position; 
         FIG. 12B  is a view showing the positional relationship between the eye of the user and each screen at the time of use of the electronic dictionary apparatus held in the portrait position; 
         FIG. 13A  is a view showing the positional relationship between the eye of the user and each screen at the time of use of an electronic dictionary apparatus according to the second embodiment held in the portrait position; 
         FIG. 13B  is a view showing the positional relationship between the eye of the user and each screen at the time of use of the electronic dictionary apparatus according to the second embodiment held in the portrait position; 
         FIG. 14A  is a view showing the positional relationship between the eye of the user and each screen at the time of use of the electronic dictionary apparatus according to the second embodiment held in the landscape position; 
         FIG. 14B  is a view showing the positional relationship between the eye of the user and each screen at the time of use of the electronic dictionary apparatus according to the second embodiment held in the landscape position; 
         FIG. 15A  is a view showing the positional relationship between the eye of the user and each screen at the time of use of the electronic dictionary apparatus according to the second embodiment held in the landscape position; and 
         FIG. 15B  is a view showing the positional relationship between the eye of the user and each screen at the time of use of the electronic dictionary apparatus according to the second embodiment held in the landscape position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
     The first embodiment in which the present invention is applied to an electronic dictionary apparatus will be described with reference to the views of the accompanying drawing. 
       FIG. 1  is a front view showing the outer arrangement of an electronic dictionary apparatus  10  according to the first embodiment. 
     The electronic dictionary apparatus  10  is configured as a portable apparatus dedicated to an electronic dictionary (to be described below) or a FDA (Personal Digital Assistants), personal computer, cellular phone terminal, electronic book, portable video game machine, or the like which has a dictionary function. 
     The electronic dictionary apparatus  10  includes a foldable case configured such that a main body case  11  and a lid case  12  can open and close relative to each other through a hinge portion  13 .  FIG. 1  shows the open state. The surface of the main body case  11  in the open state of this foldable case includes a key input unit (keyboard)  14  including character input keys, a dictionary designation key and the like, a [translate/Enter] key, a [return/list] key, cursor (↑, ↓, ←, →) keys, a [jump] key, and a loudspeaker  15  and a handwriting input unit (auxiliary screen)  16 . 
     The handwriting input unit (auxiliary screen)  16  has an integrated structure of a display unit and a touch position detection unit which detects the position touched by the user with a stylus pen, finger, or the like. A transparent touchpanel  16   t  is stacked on a 256×64 dot color liquid crystal display screen  16   d  on the middle front side of the key input unit  14 . 
     The area of the handwriting input unit (auxiliary screen)  16  is switched between a handwritten character (kanji) input area for inputting handwritten characters, an icon input area for various kinds of functions, and the like, as needed. 
     The trace of handwriting in a state in which the handwriting input unit (auxiliary screen)  16  is switched to the handwritten character input area is echoed back and displayed on the color liquid crystal display screen  16   d.    
     A 480×320 dot touchpanel color display unit (main screen)  17  with a backlight is provided on almost the entire surface of the lid case  12 . Like the handwriting input unit (auxiliary screen)  16 , the touchpanel color display unit (main screen)  17  also has an integrated structure of a display apparatus and a touch position detection apparatus which detects the position touched by the user with a stylus pen, finger, or the like. A transparent touchpanel  17   t  is stacked on a color liquid crystal display screen  17   d.    
       FIG. 2  is a block diagram showing the arrangements of electronic circuits provided in the main body case  11  and lid case  12  of the electronic dictionary apparatus  10  described above. 
     The electronic dictionary apparatus  10  reads programs recorded on various types of storage media or transmitted programs. A control computer controls the operation of the electronic dictionary apparatus  10  in accordance with the read programs. The electronic circuit of the electronic dictionary apparatus  10  includes a CPU  21 . 
     The CPU  21  is connected to a program memory (flash memory)  22  via a system bus SB. The CPU  21  controls the operation of each circuit portion by using a work memory  26  formed from an SRAM as a main memory in accordance with the apparatus control program stored in the program memory  22  in advance, the apparatus control program stored from a memory card  23  in the program memory  22  via a memory card controller  24 , or the apparatus control program stored in the program memory  22  from a Web server (in this case, a program server)  30  on Internet N via a communication control unit  25 . 
     The apparatus control program stored in the program memory  22  is activated in accordance with an input signal from the key input unit  14  according to user operation, a communication signal with each Web server  30  on the Internet N, which is connected via the communication control unit  25 , or a connection communication signal with the memory card  23  connected via the memory card controller  24 . 
     The components connected to the CPU  21  via the system bus SB include the color liquid crystal display screen  16   d , the transparent touchpanel  16   t , the color liquid crystal display screen  17   d , the transparent touchpanel  17   t , a three-axis acceleration sensor  27 , three-axis acceleration sensor  28 , and a speech synthesis unit  29 , in addition to the program memory  22 , the memory card controller  24 , the communication control unit  25 , the work memory  26 , and the key input unit  14  connected via the system bus SB. 
     The apparatus control programs stored in the program memory  22  include a dictionary database  22 A, a gamma correction table storage unit  22 B, and various types of processing programs  22 C. 
     The dictionary database  22 A includes various types of dictionary contents and dictionary name information for displaying the name of each dictionary content on the touchpanel color display unit  17 . 
     The gamma correction table storage unit  22 B stores gamma correction values for performing display operation on the color liquid crystal display screen  16   d  of the main body case  11  and the color liquid crystal display screen  17   d  of the lid case  12  in accordance with the posture angles of both the main body case  11  and the lid case  12 , as will be described later. 
     The various types of processing programs  22 C include a screen correction processing program for performing gamma correction of images to be displayed on the color liquid crystal display screen  16   d  and the color liquid crystal display screen  17   d  at the posture angles of the main body case  11  and lid case  12 , and are constituted by programs for controlling the overall operation in the electronic dictionary apparatus  10 . 
     In the specification, the processing for “gamma correction” indicates correcting the drive voltages for the color liquid crystal display screen  16   d  and the color liquid crystal display screen  17   d  using respectively gamma correction values that correspond to the posture angle of the main body case  11  and the posture angle of the lid case  12 . 
     The three-axis acceleration sensor  27  is provided on the lid case  12  to detect accelerations in the three axial directions perpendicular to each other and output them to the CPU  21 . The CPU  21  can recognize the posture of the lid case  12  from the direction of gravitational acceleration based on the outputs from the three-axis acceleration sensor  27 . 
     Likewise, the three-axis acceleration sensor  28  is provided on the main body case  11  to detect accelerations in the three axial directions perpendicular to each other and output them to the CPU  21 . The CPU  21  can recognize the posture of the main body case  11  from the direction of gravitational acceleration based on the outputs from the three-axis acceleration sensor  28 . 
     In this manner, the CPU  21  can comprehend how the user is currently using the electronic dictionary apparatus  10 , based on the posture angles of both the main body case  11  and the lid case  12 . 
     The speech synthesis unit  29  generates an analog speech signal based on text information supplied via the system bus SB and drives the loudspeaker  15  in accordance with the generated speech signal, thereby audibly outputting the corresponding information. 
     Referring to  FIG. 2  described above, the three-axis acceleration sensor  28  and the three-axis acceleration sensor  27  are provided on the main body case  11  side and the lid case  12  side, respectively, to make the CPU  21  comprehend, based on the detection outputs from the sensors, how the electronic dictionary apparatus  10  is used, from the posture angles of both the main body case  11  and the lid case  12 . 
     There is available another arrangement which detects the posture angle of one case and the angle of the hinge portion  13  to estimate the posture angle of the other case, thereby allowing to comprehend how the electronic dictionary apparatus  10  is used. 
       FIG. 3  is a block diagram showing another arrangement of the electronic circuits provided in the main body case  11  and lid case  12  of the electronic dictionary apparatus  10  described above. This arrangement includes an angle sensor  41  which detects an open angle at the hinge portion  13  in place of the three-axis acceleration sensor  27  in  FIG. 2 . 
     The angle sensor  41  is formed from a strain gauge sensor, magnetic sensor, or optical sensor. This sensor detects an open angle at the hinge portion  13  and outputs the detection result to the CPU  21 . 
     The arrangement shown in  FIG. 3  is basically the same as that shown in  FIG. 2  except that the angle sensor  41  is provided in placed of the three-axis acceleration sensor  27  in  FIG. 2 . Therefore, the same reference numerals denote the same parts, and a description of them will be omitted. 
     The operation of the above embodiment will be described next. 
     Note that in this embodiment, the basic usage patterns of the electronic dictionary apparatus  10  are as follows: using the electronic dictionary apparatus  10  while placing it on a desk or the like; holding the electronic dictionary apparatus  10  in the portrait position with the main body case  11  and the lid case  12  being open wide as shown in  FIG. 4A , that is, the way of holding the electronic dictionary apparatus  10  which is called “holding in portrait” hereinafter; and holding the electronic dictionary apparatus  10  in the landscape position with the main body case  11  and the lid case  12  being open wide as shown in  FIG. 4B , that is, the way of holding the electronic dictionary apparatus  10  which is called “holding in landscape” hereinafter. 
       FIGS. 4A and 4B  each exemplify the state in which the user holds the electronic dictionary apparatus  10  with his/her both hands, that is, a left hand LH and a right hand RH. However, the way of holding the electronic dictionary apparatus  10  is not specifically limited. 
     In “holding in portrait” shown in  FIG. 4A , the CPU  21  can comprehend the posture angles of the main body case  11  and lid case  12  from detection outputs from the three-axis acceleration sensors  28  and  27 , with the horizontal direction along the flat casing surface of each of the main body case  11  and lid case  12  being the X-axis direction, the vertical direction of the casing surface being the Y-axis direction, and the direction perpendicular to the casing surface being the Z-axis direction. 
     In “holding in landscape” shown in  FIG. 4B , the CPU  21  can comprehend the posture angles of the main body case  11  and lid case  12  from detection outputs from the three-axis acceleration sensors  28  and  27 , with the horizontal direction along the flat casing surface of each of the main body case  11  and lid case  12  being the Y-axis direction, the vertical direction of the casing surface being the X-axis direction, and the direction perpendicular to the casing surface being the Z-axis direction. 
     The following is a description of operation when using the electronic dictionary apparatus  10  while placing it on a desk or the like, in “holding in portrait” shown in  FIG. 4A , and in “holding in landscape” shown in  FIG. 4B . 
       FIG. 5  is a flowchart showing processing associated with display control on the color liquid crystal display screen  17   d  as the main screen and the color liquid crystal display screen  16   d  as the auxiliary screen, which is performed by the CPU  21  in the electronic dictionary apparatus  10  described above. 
     First of all, the CPU  21  determines whether the main body case  11  of the electronic dictionary apparatus  10  is placed on a horizontal place on, for example, a desk, by determining whether a detection output from the three-axis acceleration sensor  28  provided on the main body case  11  side, on which the handwriting input unit (auxiliary screen)  16  exists, in the Z-axis direction is almost equal to the gravitational acceleration component, and its displacement angle is almost zero (step S 101 ). 
     In this case, upon determining that the detection output from the three-axis acceleration sensor  28  in the Z-axis direction is almost equal to the gravitational acceleration component and the main body case  11  of the electronic dictionary apparatus  10  is placed on a flat place, the CPU  21  detects an angle θ of the touchpanel color display unit (main screen)  17  relative to the handwriting input unit (auxiliary screen)  16  from detection outputs from the three-axis acceleration sensor  27  provided on the lid case  12  side, on which the touchpanel color display unit (main screen)  17  exists, in the Y-axis and Z-axis directions (step  102 ). 
     The CPU  21  then calculates an angle θ′ of the touchpanel color display unit (main screen)  17  from the detected angle θ according to (180°−θ), and reads gamma correction values for the touchpanel color display unit (main screen)  17  and the handwriting input unit (auxiliary screen)  16  from the gamma correction table storage unit  22 B based on the calculated angle θ′ of the handwriting input unit (auxiliary screen)  16  (step S 103 ). 
       FIG. 6A  exemplifies a gamma correction value table for the main screen and the auxiliary screen which is used when the user uses the electronic dictionary apparatus  10  in the stationary position and is stored in the gamma correction table storage unit  22 B of the program memory  22 . As shown in  FIG. 6A , this table stores gamma correction values α and α′ for the main screen and auxiliary screen in increments of 1° as the display angle θ′ of the main screen changes from 0 to 90°. 
     The CPU  21  executes gamma correction in display driving on the color liquid crystal display screen  17   d  and the color liquid crystal display screen  16   d  based on the gamma correction values α and α′ read in this manner (step S 104 ). The process then returns to the processing starting from step S 101 . 
       FIGS. 7A and 7B  are views each showing a case in which the positional relationship between an eye UE of the user and each screen is viewed laterally when the user uses the electronic dictionary apparatus  10  in the stationary position. 
       FIG. 7A  shows a state in which the lid case  12  on which the main screen exists is slightly raised. The open angle θ of the lid case  12  relative to the main body case  11  is about 135°, and the display angle θ′ of the main screen is about 45°. Assume that the position of the eye UE of the user is set in advance to 20 cm to the front side of the main body case  11  and 40 cm above it. 
     When viewing the main screen  17   d  from the eye UE of the user, the downward viewing angle required for the main screen  17   d  is (90°−θm), where θm is the interior angle defined by the line of sight of the eye and the main screen  17   d.    
     When viewing the auxiliary screen  16   d  from the eye UE of the user, the downward viewing angle required for the auxiliary screen  16   d  is (θs−90°, where θs is the interior angle defined by the line of sight of the eye and the auxiliary screen  16   d.    
     The CPU  21  reads the gamma correction values α and α′ from the gamma correction table storage unit  22 B stored in advance in accordance with the viewing angles of the main screen and auxiliary screen assumed in the above manner, and executes gamma correction in display driving on the main screen  17   d  and the auxiliary screen  16   d  based on the read gamma correction values α and α′, thereby reliably positioning the user within the viewing angle. 
       FIG. 7B  shows a state in which the lid case  12  side on which the main screen exists is laid down like the main body case  11  side on which the auxiliary screen exists. The open angle θ of the lid case  12  relative to the main body case  11  is 180°, and the display angle θ′ of the main screen is 0°. 
     The CPU  21  reads the gamma correction values α and α′ from the gamma correction table storage unit  22 B and executes gamma correction in display driving on the main screen  17   d  and the auxiliary screen  16   d  based on the read gamma correction values α and α′, thereby adjusting the two screens so as to reliably position the user within the viewing angle. 
     Upon determining in step S 101  in  FIG. 5  that the detection output from the three-axis acceleration sensor  28  in the Z-axis direction differs from the gravitational acceleration component and the main body case  11  of the electronic dictionary apparatus  10  is not horizontal, the CPU  21  determines that the user is holding the electronic dictionary apparatus  10  in the portrait position or the landscape position. The CPU  21  then determines whether the user is using the electronic dictionary apparatus  10  while holding the main body case  11  in the landscape position shown in  FIG. 4B , by determining whether the detection output from the three-axis acceleration sensor  27  on the lid case  12  side, on which the main screen  17   d  exists, in the X-axis direction is almost equal to the gravitational acceleration component and the displacement angle is almost zero (step S 105 ). 
     In this case, upon determining that the detection output from the three-axis acceleration sensor  27  in the X-axis direction differs from the gravitational acceleration component and the displacement angle is almost equal to 90°, the CPU  21  determines that the user is holding the electronic dictionary apparatus  10  in the portrait position shown in  FIG. 4A  instead of the landscape position. The CPU  21  then calculates the tilt state of the touchpanel color display unit (main screen)  17  from the detection outputs from the three-axis acceleration sensor  27  provided on the lid case  12  side, on which the touchpanel color display unit (main screen)  17  exists, in the Y-axis and Z-axis directions (step S 106 ). 
     The CPU  21  calculates the tilt state of the handwriting input unit (auxiliary screen)  16  from the detection outputs from the three-axis acceleration sensor  28  provided on the main body case  11  side, on which the handwriting input unit (auxiliary screen)  16  exists, in the Y-axis and Z-axis directions (step S 107 ). 
     Based on the tilts of the touchpanel color display unit (main screen)  17  and handwriting input unit (auxiliary screen)  16  calculated by the processing in steps S 106  and S 107 , the CPU  21  calculates the open angle θ of the lid case  12  relative to the main body case  11  from these positional relationships (step S 106 ). 
     The CPU  21  then reads gamma correction values for the touchpanel color display unit (main screen)  17  and the handwriting input unit (auxiliary screen)  16  from the gamma correction table storage unit  22 B based on the calculated angle θ (step S 109 ). 
       FIG. 6B  exemplifies a gamma correction value table for the main screen and the auxiliary screen which is used when the user uses the electronic dictionary apparatus  10  while holding it in the portrait position and is stored in the gamma correction table storage unit  22 B of the program memory  22 . As shown in  FIG. 6B , this table stores gamma correction values β and β′ for the main screen and auxiliary screen in increments of 1° as the display angle θ′ between the two display screens, namely the main screen and the auxiliary screen, changes from 90° to 180°. 
     The CPU  21  executes gamma correction in display driving on the color liquid crystal display screen  17   d  and the color liquid crystal display screen  16   d  based on the gamma correction values β and β′ read in this manner (step S 104 ). The process then returns to the processing starting from step S 101 . 
       FIGS. 8A and 8B  are views each showing a case in which the positional relationship between the eye UE of the user and each screen is viewed laterally when the user uses the electronic dictionary apparatus  10  while holding it in the portrait position. 
       FIG. 8A  shows a state in which the lid case  12  side (θ) on which the main screen exists is open at about 135° relative to the main body case  11  on which the auxiliary screen exists. 
       FIG. 8B  shows a case in which the open angle θ of the lid case  12  relative to the main body case  11  is set to 180° so as to make the lid case  12  side, on which the main screen exists, flush with the main body case  11  when the user uses the electronic dictionary apparatus  10  while holding it in the portrait position. 
     The CPU  21  reads the gamma correction values β and β′ from the gamma correction table storage unit  22 B described above, and executes gamma correction in display driving on the main screen  17   d  and the auxiliary screen  16   d  based on the read gamma correction values β and β′, thereby adjusting the display tones of the two screens so as to reliably position the eye UP of the user within the viewing angle. 
     In addition, upon determining in step S 105  that the detection output from the three-axis acceleration sensor  27  on the lid case  12  side, on which the main screen  17   d  exists, is almost equal to the gravitational acceleration component, and the displacement angle is almost zero, the CPU  21  determines that the user is holding the electronic dictionary apparatus  10  in the landscape position shown in  FIG. 4B . The CPU  21  then calculates the tilt state of the touchpanel color display unit (main screen)  17  from the detection outputs from the three-axis acceleration sensor  27  provided on the lid case  12  side, on which the touchpanel color display unit (main screen)  17  exists, in the X-axis and Z-axis directions (step S 110 ). 
     The CPU  21  calculates the tilt state of the handwriting input unit (auxiliary screen)  16  from the detection outputs from the three-axis acceleration sensor  28  provided on the main body case  11  side, on which the handwriting input unit (auxiliary screen)  16  exists, in the X-axis and Z-axis directions (step S 111 ). 
     Based on the tilts of the touchpanel color display unit (main screen)  17  and handwriting input unit (auxiliary screen)  16  calculated by the processing in steps S 110  and S 111 , the CPU  21  calculates the open angle θ of the lid case  12  relative to the main body case  11  from these positional relationships (step S 112 ). 
     The CPU  21  then reads gamma correction values for the touchpanel color display unit (main screen)  17  and the handwriting input unit (auxiliary screen)  16  from the gamma correction table storage unit  22 B based on the calculated angle θ (step S 113 ). 
       FIG. 6C  exemplifies a gamma correction value table for the main screen and the auxiliary screen which is used when the user uses the electronic dictionary apparatus  10  while holding it in the landscape position and is stored in the gamma correction table storage unit  22 B of the program memory  22 . As shown in  FIG. 6C , this table stores gamma correction values δ and δ′ for the main screen and auxiliary screen in increments of 1° as the display angle θ′ between the two display screens, namely the main screen and the auxiliary screen, changes from 90 to 180°. 
     The CPU  21  executes gamma correction in display driving on the color liquid crystal display screen  17   d  and the color liquid crystal display screen  16   d  based on the gamma correction values δ and δ′ read in this manner (step S 104 ). The process then returns to the processing starting from step S 101 . 
       FIGS. 9A and 9B  are views each showing a case in which the positional relationship between the eye UE of the user and each screen is viewed from above when the user uses the electronic dictionary apparatus  10  while holding it in the landscape position. 
       FIG. 9A  shows a state in which the lid case  12  side (θ) on which the main screen exists is open at about 135° relative to the main body case  11  on which the auxiliary screen exists. 
       FIG. 9B  shows a case in which the open angle θ of the lid case  12  relative to the main body case  11  is set to 180° so as to make the lid case  12  side, on which the main screen exists, flush with the main body case  11  on which the auxiliary screen exists. 
     The CPU  21  reads the gamma correction values δ and δ′ from the gamma correction table storage unit  22 B and executes gamma correction in display driving on the main screen  17   d  and the auxiliary screen  16   d  based on the read gamma correction values δ and δ′, thereby adjusting the display tones of the two screens so as to reliably position the eye UE of the user within the viewing angle. 
     Assume that in the use of the electronic dictionary apparatus  10  while being held in the landscape position, gamma correction values are set and stored in the gamma correction table storage unit  22 B assuming that the eye (the dominant eye, in particular) UE of the user is located at the front of the touchpanel color display unit (main screen)  17  as shown in  FIGS. 9A and 9B . 
     The CPU  21  therefore executes display control by the above gamma correction so as to set a smaller viewing angle on the touchpanel color display unit (main screen)  17  on the lid case  12  side, while executing display control so as to set a wider viewing angle on the handwriting input unit (auxiliary screen)  16  on the main body case  11  side. 
     As described above in detail, according to this embodiment, it is possible to ensure optical visual fields on both the touchpanel color display unit (main screen)  17  on the lid case  12  side and the handwriting input unit (auxiliary screen)  16  on the main body case  11  side in either of the cases in which the user uses the electronic dictionary apparatus  10  in the stationary position, in the portrait position, and in the landscape position. 
     In addition, according to the above embodiment, as shown in  FIGS. 6A ,  6 B, and  6 C, the tables store gamma correction values for display control on the two screens in correspondence with the respective cases in which the user uses the electronic dictionary apparatus  10  in the stationary position, in the portrait position, and in the landscape position, while the range of the open angles θ which the lid case  12  on which the main screen  17  is provided can take with respect to the main body case  11  on which the auxiliary screen exists is limited to, for example, 90 to 180°. 
     Storing only necessary gamma correction values in the tables in this manner in consideration of assumed usages makes it possible to decrease the capacity of the tables required for control and reduce the circuit size and the load on control programs. 
     Second Embodiment 
     The second embodiment in which the present invention is applied to an electronic dictionary apparatus will be described below with reference to the views of the accompanying drawing. 
     The outer arrangement of an electronic dictionary apparatus  10 ′ according to this embodiment is basically the same as that shown in  FIG. 1 , and the arrangements of electronic circuits provided in a main body case  11  and lid case  12  of the electronic dictionary apparatus  10 ′ are basically the same as those shown in  FIG. 3 . Therefore, the same reference numerals denote the same parts, and an illustration and description of them will be omitted. 
     The operation of the above embodiment will be described next. 
     In this embodiment, the user basically uses the electronic dictionary apparatus  10 ′ in either of the following forms: using the apparatus while holding it in the portrait position with the main body case  11  and the lid case  12  being wide open as shown in  FIG. 4A ; and using the apparatus while holding it in the landscape position with the main body case  11  and the lid case  12  being wide open as shown in  FIG. 4B . 
     The operation of the electronic dictionary apparatus  10 ′ in a case in which the user uses the apparatus while holding it in the portrait position or landscape position will be described below. 
       FIG. 10  is a flowchart showing processing associated with display control on a color liquid crystal display screen  17   d  as a main screen and a color liquid crystal display screen  16   d  as an auxiliary screen, which is performed by a CPU  21  in the electronic dictionary apparatus  10 ′. 
     First of all, the CPU  21  detects an open angle between the lid case  12  having a main screen and the main body case  11  having an auxiliary screen based on an output from an angle sensor  41  (step S 301 ). 
     The CPU  21  then determines whether the main body case  11  of the electronic dictionary apparatus  10 ′ is placed on a horizontal place on, for example, a desk, by determining whether a detection output from a three-axis acceleration sensor  28  provided on the main body case  11  side in the Z-axis direction is almost equal to the gravitational acceleration component, and its displacement angle is almost zero (step S 302 ). 
     In this case, upon determining that the detection output from the three-axis acceleration sensor  28  in the Z-axis direction is almost equal to the gravitational acceleration component and the main body case  11  of the electronic dictionary apparatus  10 ′ is placed on a flat place, the CPU  21  performs processing similar to that in step S 103  and the subsequent steps in  FIG. 5  described above. A detailed description of the subsequent processing will be omitted in this embodiment. 
     Upon determining in step S 302  that the main body case  11  is not placed on a horizontal place, the CPU  21  determines whether the main body case  11  of the electronic dictionary apparatus  10 ′ is held in the landscape position shown in  FIG. 4B , by determining whether the detection output from the three-axis acceleration sensor  28  provided on the main body case  11  side in the X-axis direction is almost equal to the gravitational acceleration component and its displacement angle is almost zero (step S 303 ). 
     In this case, the CPU  21  determines that the electronic dictionary apparatus  10 ′ is held in the landscape position, only when the detection output from the three-axis acceleration sensor  28  in the X-axis direction is almost equal to the gravitational acceleration component and its displacement angle is almost zero, and changes/sets characters to be displayed to those for “holding in landscape” on both the color liquid crystal display screen  17   d  as a main screen and the color liquid crystal display screen  16   d  as an auxiliary screen (step S 304 ). 
     The CPU  21  does not perform the processing in step S 304  if the CPU  21  determines that the electronic dictionary apparatus  10 ′ is not held in the landscape position. 
     Subsequently, the CPU  21  determines, based on the presence/absence of an output from a transparent touchpanel  17   t  of a touchpanel color display unit (main screen)  17 , whether the user has touched the main screen (step S 305 ). 
     Upon determining that the user has touched the screen, the CPU  21  determines that an eye UE of the user is located at the front of the touchpanel color display unit (main screen)  17 , and sets an interior angle θm defined by the main screen and the eye UE of the user to 90° (step S 306 ). 
     The CPU  21  then calculates and sets an interior angle θs defined by the auxiliary screen and the eye UE of the user according to (225°−θ) by using the value of an open angle θ between the main body case  11  and the lid case  12  obtained in immediately preceding step S 301  (step S 307 ). 
     Subsequently, the CPU  21  refers to a gamma correction table storage unit  22 B with the angle θm on the main screen side and the angle θs on the auxiliary screen side, which are obtained above, reads corresponding gamma correction values αm and αs, and executes gamma correction in display driving on the color liquid crystal display screen  17   d  and the color liquid crystal display screen  16   d  (step S 308 ). The process then returns to processing starting from step S 301  described above. 
       FIG. 11A  exemplifies a table of gamma correction values associated with the interior angles θm indicating the positions/directions of the eye UE of the user relative to the main screen and is stored in the gamma correction table storage unit  22 B of a program memory  22 . As shown in  FIG. 11A , this table stores gamma correction values αm in increments of 1° as the angle θm defined by the main screen and the eye UE of the user changes from 0° to 150°. 
       FIG. 11B  exemplifies a table of gamma correction values associated with the interior angles θs indicating the positions/directions of the eye UE of the user relative to the auxiliary screen and is stored in the gamma correction table storage unit  22 B of the program memory  22 . As shown in  FIG. 11B , this table stores gamma correction values as in increments of 1° as the angle θs defined by the auxiliary screen and the eye UE of the user changes from 0° to 150°. 
       FIGS. 12A and 12B  are views each showing a case in which the positional relationship between the eye UE of the user and each screen is viewed laterally when the user uses the electronic dictionary apparatus  10 ′ while holding it in the portrait position and touches the transparent touchpanel  17   t  on the main screen side. Assume that in  FIGS. 12A and 12B , the user touches the transparent touchpanel  17   t  with a stylus pen SP, and the angle of each screen is estimated, assuming that the distance between the main screen  17  and the eye UE of the user is a distance specified in advance, for example, about 40 cm. 
       FIG. 12A  shows a state in which the lid case  12  on which the main screen exists is open at an angle of about 135° relative to the main body case  11  on which the auxiliary screen exists. Letting θv be a line-of-sight angle which moves when the eye UE of the user sees the main screen  17  and an auxiliary screen  16 , the following equation holds:
 
θ+θ m+θs+θv= 360° (the sum of the interior angles of a rectangle)
 
     If, therefore, for example, θm=90° and θv=45′, θs=225°−θ. It is possible to uniquely derive an interior angle θs defined between the eye UE of the user and the auxiliary screen  16  from a detection output from the angle sensor  41 . 
       FIG. 12B  shows a case in which the open angle θ of the lid case  12  relative to the main body case  11  is set to 180° so as to make the lid case  12  side, on which the main screen exists, flush with the main body case  11  on which the auxiliary screen exists. 
     In either of the cases shown in  FIGS. 12A and 12B , the CPU  21  estimates the interior angle θs between the auxiliary screen and the line of sight of the eye UE of the user, assuming from touching operation on the transparent touchpanel  17   t  on the main screen side that the eye UE of the user is located at the front of the main screen and the interior angle between the main screen and the eye UE of the user is 90° and that the distance between the main screen  17  and the eye UE of the user is specified as described above. 
       FIGS. 14A and 14B  are views each showing a case in which the positional relationship between the eye UE of the user and each screen is viewed from above when the user uses the electronic dictionary apparatus  10 ′ while holding it in the landscape position and touches the transparent touchpanel  17   t  on the main screen side. Assume that in  FIGS. 14A and 14B , the user touches the transparent touchpanel  17   t  with the stylus pen SP, and the angle of each screen is estimated, assuming that the distance between the main screen  17  and the eye UE of the user is a distance specified in advance, for example, about 40 cm. 
       FIG. 14A  shows a state in which the lid case  12  on which the main screen exists is open at an angle of about 13.5° relative to the main body case  11  on which the auxiliary screen exists. 
       FIG. 14B  shows a case in which the open angle θ of the lid case  12  relative to the main body case  11  is set to 180° so as to make the lid case  12  side, on which the main screen exists, flush with the main body case  11  on which the auxiliary screen exists. 
     In either of the cases shown in  FIGS. 14A and 14B , the CPU  21  estimates the interior angle θs between the auxiliary screen and the eye UE of the user, assuming from touching operation on the transparent touchpanel  17   t  on the main screen side that the eye UE of the user is located at the front of the main screen and the interior angle between the main screen and the eye UE of the user is 90° and that the distance between the main screen  17  and the eye UE of the user is specified as described above. 
     The CPU  21  reads gamma correction values αm and αs from the gamma correction table storage unit  22 B described above and executes gamma correction in display driving on the main screen  17   d  and the auxiliary screen  16   d  based on the read gamma correction values αm and αs, thereby adjusting the display tones of the two screens so as to reliably position the eye UE of the user within the viewing angle. 
     Upon determining in step S 305  that the user has not touched the main screen, the CPU  21  determines, based on the presence/absence of an output from the transparent touchpanel  16   t  of the handwriting input unit (auxiliary screen)  16 , whether the user has touched the auxiliary screen (step S 309 ). 
     Upon determining that the user has touched the auxiliary screen, the CPU  21  sets the interior angle θs defined between the auxiliary screen and the eye UE of the user to 90°, assuming that the eye UE of the user is located at the front of the handwriting input unit (auxiliary screen)  16  (step S 310 ). 
     The CPU  21  then calculates and sets the interior angle θm between the main screen and the eye UE of the user according to (225°−θ) by using the value of the open angle θ between the main body case  11  and the lid case  12 , which is obtained in immediately preceding step S 301  (step S 311 ). 
     The CPU  21  then refers to the gamma correction table storage unit  22 B with the angle θm on the main screen side and the angle θs on the auxiliary screen side, which are obtained above, reads corresponding gamma correction values αm and αs, and executes gamma correction in display driving on the color liquid crystal display screen  17   d  and the color liquid crystal display screen  16   d  (step S 308 ). The process then returns to processing starting from step S 301  described above. 
       FIGS. 13A and 13B  are views each showing a case in which the positional relationship between the eye UE of the user and each screen is viewed laterally when the user uses the electronic dictionary apparatus  10 ′ while holding it in the portrait position and touches the transparent touchpanel  16   t  on the auxiliary screen side. Assume that in  FIGS. 13A and 13B , the user touches the transparent touchpanel  16   t  with the stylus pen SP, and the angle of each screen is estimated, assuming that the distance between the auxiliary screen  16  and the eye UE of the user is a distance specified in advance, for example, about 40 cm. 
       FIG. 13A  shows a state in which the lid case  12  on which the main screen exists is open at an angle of about 135° relative to the main body case  11  on which the auxiliary screen exists. 
       FIG. 13B  shows a case in which the open angle θ of the lid case  12  relative to the main body case  11  is set to 180° so as to make the lid case  12  side, on which the main screen exists, flush with the main body case  11  on which the auxiliary screen exists. 
     In either of the cases shown in  FIGS. 13A and 13B , the CPU  21  estimates the interior angle θm between the main screen and the eye UE of the user, assuming from touching operation on the transparent touchpanel  16   t  on the auxiliary screen side that the eye UE, of the user is located at the front of the auxiliary screen and the interior angle between the main screen and the eye UE of the user is 90° and that the distance between the auxiliary screen  16  and the eye UE of the user is specified as described above. 
       FIGS. 15A and 15B  are views each showing a case in which the positional relationship between the eye UE of the user and each screen is viewed from above when the user uses the electronic dictionary apparatus  10 ′ while holding it in the landscape position and touches the transparent touchpanel  16   t  on the auxiliary screen side. Assume that in  FIGS. 15A and 15B , the user touches the transparent touchpanel  16   t  with the stylus pen SP, and the angle of each screen is estimated, assuming that the distance between the auxiliary screen  16  and the eye UE of the user is a distance specified in advance, for example, about 40 cm. 
       FIG. 15A  shows a state in which the lid case  12  on which the main screen exists is open at an angle of about 135° relative to the main body case  11  on which the auxiliary screen exists. 
       FIG. 15B  shows a case in which the open angle θ of the lid case  12  relative to the main body case  11  is set to 180° so as to make the lid case  12  side, on which the main screen exists, flush with the main body case  11  on which the auxiliary screen exists. 
     In either of the cases shown in  FIGS. 15A and 15B , the CPU  21  estimates the interior angle θm between the main screen and the eye UE of the user, assuming from touching operation on the transparent touchpanel  16   t  on the auxiliary screen side that the eye UE of the user is located at the front of the auxiliary screen and the interior angle between the auxiliary screen and the eye UE of the user is 90° and that the distance between the auxiliary screen  16  and the eye UE of the user is specified as described above. 
     The CPU  21  reads gamma correction values αm and αs from the gamma correction table storage unit  22 B described above and executes gamma correction in display driving on the main screen  17   d  and the auxiliary screen  16   d  based on the read gamma correction values αm and αs, thereby adjusting the display tones of the two screens so as to reliably position the eye UE of the user within the viewing angle. 
     Upon determining in step S 309  that the user has not touched the auxiliary screen, the CPU  21  determines that the user has touched neither the main screen  17  nor the auxiliary screen  16 , and reads θm and θs corresponding to the value of the open angle θ of the hinge portion  13  detected in immediately preceding step S 301  from the gamma correction table storage unit  22 B of the program memory  22  (step S 312 ). 
       FIG. 11C  exemplifies a table indicating the estimated values of the line-of-sight angle θm on the main screen and the line-of-sight angle θs on the auxiliary screen which correspond to the open angle θ without touching operation, which are stored in the gamma correction table storage unit  22 B in advance. This table stores θm and θs in increments of 1° as the open angle θ changes from 90 to 180° when the user uses the electronic dictionary apparatus  10 ′ while holding it in the portrait position or the landscape position and mainly sees the touchpanel color display unit (main screen)  17  on the lid case  12  side, with the distance between the eye UE of the user and the main screen being held at a typical distance, for example, 30 cm. 
     Upon reading the estimated values of θm and θs corresponding to the open angle θ without touching operation from the gamma correction table storage unit  22 B, the CPU  21  reads first the gamma correction value αm for the main screen from the table shown in  FIG. 11A  in the gamma correction table storage unit  22 B according to the estimated value of the interior angle θm between the main screen  17  and the line of sight of the user (step S 313 ). 
     The CPU  21  then reads the gamma correction value αs for the auxiliary screen from the table shown in  FIG. 11B  in the gamma correction table storage unit  22 B according to the estimated value of the interior angle θs between the auxiliary screen  16  and the line of sight of the user in the same manner (step S 314 ). 
     The CPU  21  executes gamma correction in display driving on the color liquid crystal display screen  17   d  and the color liquid crystal display screen  16   d  by using the obtained gamma correction values αm and αs (step  308 ). The process then returns to the processing starting from step S 301 . 
     As has been described above in detail, both the touchpanel color display unit (main screen)  17  and the handwriting input unit (auxiliary screen)  16  include the transparent touchpanels  17   t  and  16   t  which allow the user to perform input operation by touching operation, and this apparatus is configured to perform gamma correction on the respective display units, assuming that when touching operation on one of the panels is detected, the eye UE of the user is located at the front of the panel. This makes it possible to execute accurate gamma correction in consideration of operability in actual operation and ensure optimal visual field for the user. 
     The above embodiments have exemplified the touchpanel color display unit (main screen)  17  and the handwriting input unit (auxiliary screen)  16 , both of which are configured to allow to input operation by touching operation. However, the present invention is not limited to this. As long as at least one of a plurality of display units includes a transparent touchpanel, it is possible to implement display in an optimal visual field for the user by performing the same control as that described above when the user performs touching operation on the touchpanel. 
     Furthermore, the present invention is not limited to each embodiment described above, and can be variously modified in the execution stage within the spirit and scope of the invention. In addition, the functions implemented in the above embodiments may be executed in proper combinations if possible. The above embodiments include inventions of various stages, and various inventions can be extracted by proper combinations of a plurality of disclosed constituent elements. Even if several constituent elements are omitted from all the constituent elements in each embodiment, the arrangement from which these constituent elements are omitted can be extracted as an invention. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.