Abstract:
There is provided a method for controlling a determining apparatus including: a first pixel for displaying a first image; a second pixel for displaying a second image; a light shielding member that allows the first image to be viewed from a first direction and blocks the first image from a second direction, and allows the second image to be viewed from the second direction and blocks the second image from the first direction; a first sensor provided for the first pixel and detecting the quantity of light coming from the first direction; and a second sensor provided for the second pixel and detecting the quantity of light coming from the second direction. The method includes: storing at least one frame of the results of detection of the first and second sensors; and after obtaining the present results of detection of the first and second sensors, determining whether an object approaches from the first direction or the second direction from the result of comparison between the stored detection results of one frame and the results of detection of present one frame.

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a technique for discriminating between operations from different directions on a display screen. 
     2. Related Art 
     Display panels having a so-called dual image display mode have recently become popular in which different images can be viewed from two directions. To provide an information input capability to such display panels having a two-screen display mode, it is necessary to discriminate between input operations, because the input operations are made from two directions. 
     There is therefore proposed a technique for determining the direction of the viewer by displaying icons corresponding to two screens so as not to agree with each other and by detecting an operated icon (for example, refer to JP-A-2005-284592). 
     However, in the above-described technique, the direction of operation is determined from the position of the icon touched. Accordingly, the proximity of icons corresponding to two screens may cause misidentification. To prevent it, it is necessary for the above technique to display the two icons in different positions as far as possible, thus resulting in limitations to the display screen. 
     SUMMARY 
     An advantage of some aspects of the invention is that a determining apparatus capable of direct determination of the direction of input operation and a method for controlling the same are provided. 
     According to a first aspect of the invention, there is provided a method for controlling a determining apparatus including: first pixels for displaying a first image; second pixels for displaying a second image; a light shielding member that allows the first image to be viewed from a first direction and blocks the first image from a second direction, and allows the second image to be viewed from the second direction and blocks the second image from the first direction; a first sensor provided for at least one of the first pixels and detecting the quantity of light coming from the first direction; and a second sensor provided for at least one of the second pixels and detecting the quantity of light coming from the second direction. The method includes: obtaining a first detection result of the first sensor and a second detection result of the second sensor during a first time; obtaining a third detection result of the first sensor and a fourth detection result of the second sensor during a second time after the first time; obtaining a first result by comparing the third detection result with the first detection result; obtaining a second result by comparing the fourth detection result with the second detection result; and determining whether an object is approaching from the first direction or from the second direction based on the first result and the second result. This invention allows direct determination of whether an object approaches from the first direction or the second direction from the results of detection by the first and second sensors. 
     It is preferable that, in the step of obtaining the first result, determining a shrinkage ratio in quantity of light detected by the first sensor between the first detection result and the third detection result, in the step of obtaining the second result, determining a shrinkage ratio in quantity of light detected by the second sensor between the second detection result and the fourth detection result, and in the step of determining, comparing the first result and the second result to determine whether a shrinkage ratio is greater for the first sensor or for the second sensor, determining that an object is approaching from the first direction when the shrinkage ratio is greater for the first sensor than for the second sensor, and determining that an object is approaching from the second direction when the shrinkage ratio is greater for the second sensor than for the first sensor. 
     It is preferable that, in the step of obtaining the first result, determining a shift amount of gravity center in quantity of light detected by the first sensor between the first detection result and the third detection result, in the step of obtaining the second result, determining a shift amount of gravity center in quantity of light detected by the second sensor between the second detection result and the fourth detection result, and in the step of determining, comparing the first result and the second result to determine whether a shift amount of gravity center is greater for the first sensor or for the second sensor, determining that an object is approaching from the first direction when the shift amount is smaller for the first sensor than for the second sensor, and determining that an object is approaching from the second direction when the shift amount is smaller for the second sensor than for the first sensor. 
     It is preferable that, in the step of determining by comparing the first result and the second result, determining that an object is approaching from the center between the first direction and the second direction when the shift in quantity of light detected by the first sensor between the first detection result and the third detection result being symmetrical to the shift in quantity of light detected by the second sensor between the second detection result and the fourth detection result. 
     It is preferable that the first image and/or the second image be controlled according to an approaching direction determined. According to a second aspect of the invention, there is provided a method for controlling a determining apparatus including: first pixels for displaying a first image; second pixels for displaying a second image; a light shielding member that allows the first image to be viewed from a first direction and blocks the first image from a second direction, and allows the second image to be viewed from the second direction and blocks the second image from the first direction; first sensors provided for the first pixels, the first sensors being detecting the quantity of light coming from the first direction and including a third sensor that is provided adjacent to the first direction and a fourth sensor that is provided adjacent to the second direction; and second sensors provided for the second pixels, the second sensors being detecting the quantity of light coming from the second direction and including a fifth sensor that is provided adjacent to the first direction and a sixth sensor that is provided adjacent to the second direction. The first and second sensors being arranged in a matrix matter. The method includes: obtaining a first detection result of the fourth sensor and a second detection result of the fifth sensor during a first time; obtaining a third detection result of the fourth sensor and a fourth detection result of the fifth sensor during a second time after the first time; and in the case that there is a difference between the second detection result and the fourth detection result, determining that an object is approaching from the first direction, and in the case that there is a difference between the first detection result and the third detection result, determining that an object is approaching from the second direction. 
     It is preferable that, in the case that there is a difference between the second detection result and the fourth detection result, detecting the quantity of light by using the first sensors, and in the case that there is a difference between the first detection result and the third detection result, detecting the quantity of light by using the second sensors. 
     According to a third aspect of the invention, there is provided a method for controlling a determining apparatus including: first pixels for displaying a first image; second pixels for displaying a second image; a light shielding member that allows the first image to be viewed from a first direction and blocks the first image from a second direction, and allows the second image to be viewed from the second direction and blocks the second image from the first direction; a first sensor provided for the first pixel and detecting the quantity of light coming from the first direction; and a second sensor provided for the second pixel and detecting the quantity of light coming from the second direction. The method includes: storing at least one frame of the results of detection of the first and second sensors; and after obtaining the present results of detection of the first and second sensors, determining whether an object approaches from the first direction or the second direction from the result of comparison between the stored detection results of one frame and the results of detection of present one frame. This invention allows direct determination of whether an object approaches from the first direction or the second direction from the results of detection by the first and second sensors. 
     It is preferable that, for each of the results of detection by the first sensor and the second sensor, one frame of the stored results and one frame of the present results be compared to determine that an object approaches from the direction corresponding to the detection results in which the area of the light-quantity changed portion is smaller. It is preferable that, for each of the results of detection by the first sensor and the second sensor, one frame of the stored results and one frame of the present results be compared to determine that an object approaches from the direction corresponding to the detection results in which the shift of the center of gravity of the light-quantity changed portion is smaller. 
     It is preferable that, in the first and second matrix sensors, when one of the outermost two sides adjacent to the first direction and the outermost two sides adjacent to the second direction has changed in the quantity of light, it be determined that an object approaches from the other of the first and second directions. 
     It is preferable that, in the first and second matrix sensors, the quantity of light be detected by the outermost two sides adjacent to the first direction and the outermost two sides adjacent to the second direction; when the pixels on one of the sides adjacent to the first and second directions have changed in the quantity of light, it be determined that an object approaches from the other of the first and second directions; and thereafter the quantity of light be determined by one of the first and second sensors. 
     It is preferable that, for each of the results of detection by the first sensor and the results of detection by the second sensor, one frame of the stored results and one frame of the present results be compared, wherein when the light-quantity changed portions are in symmetry, it be determined that an object approaches from the center. 
     It is preferable that a first image and/or a second image be controlled according to an approaching direction determined. 
     The invention can be applied not only to a method for controlling a determining apparatus but also to a determining apparatus capable of display. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a diagram showing the structure of a display device according to a first embodiment of the invention. 
         FIG. 2  is a diagram of one example of the pixels of the display device. 
         FIG. 3  is a diagram showing the relationship between the pixels and the optical members of the display device. 
         FIG. 4  is a diagram showing the optical paths of the display device. 
         FIG. 5  is a flowchart for the process for determination of operation on the display device. 
         FIG. 6  is a diagram showing the process for determination of operation on the display device. 
         FIG. 7A  is a diagram showing the process for determination of operation on the display device. 
         FIG. 7B  is a diagram showing the process for determination of operation on the display device. 
         FIG. 8  is a flowchart for the process for determination of operation on the display device according to the first embodiment. 
         FIG. 9  is a diagram showing the structure of a display device according to a second embodiment. 
         FIG. 10  is a flowchart for the process for determination of operation on the display device. 
         FIG. 11  is a diagram showing the process for determination of operation on the display device. 
         FIG. 12  is a flowchart for the process for determination of operation on a display device according to a third embodiment. 
         FIG. 13  is a diagram showing the process for determination of operation on the display device. 
         FIG. 14A  is a diagram showing the process for determination of operation on the display device. 
         FIG. 14B  is a diagram showing the process for determination of operation on the display device. 
         FIG. 15  is a diagram showing another relationship between the pixels and the optical members of the display device. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Embodiments of the invention will be described with reference to the drawings. 
     First Embodiment 
     A display device according to a first embodiment of the invention will first be described. The display device is, for example, the display of a car navigation system, which is located in the center of the dashboard of a vehicle and capable of displaying different images for the driver seat and the passenger seat. 
     In this description, the driver seat is on the right (the passenger seat is on the left) in the direction of travel of the vehicle, with right-hand drive cars as the reference. Conversely, as viewed from the direction of the display, the driver seat is on the left (the passenger seat is on the right). 
       FIG. 1  shows the structure of the display device  1 . Of the components of car navigation systems, components other than those for display and input are omitted here because they have no direct relation to the invention. 
     As shown in  FIG. 1 , the display device  1  includes a control circuit  10 , a Y driver  12 , an X driver  14 , a Y driver  16 , a read circuit  18 , a determining circuit  20 , and a display panel  100 . Among them, the display panel  100  of this embodiment has a matrix array in which pixels L for displaying an image to be viewed from the driver seat and pixels R for displaying an image to be viewed from the passenger seat are disposed alternately in a striped pattern. 
     There is no difference in structure between the pixels L and the pixels R; a mere difference is the sources of images to be displayed by those pixels. They are therefore simply referred to as pixels  110  if there is no need to discriminate between them. 
     Referring now to  FIG. 2 , the pixels  110  will be described. 
     While the pixels  110  are actually arrayed in matrix form as shown in  FIG. 1 ,  FIG. 2  shows any one of the pixels arrayed in matrix form. 
     One scanning line  112  extending in the X direction is shaped by one row of the matrix of pixels  110 , and one data line  114  extending in the Y direction is shared by one column of the pixels  110 . Similarly, control lines  142  and  143  extending in the X direction are shared by one row of the pixels  110 , and one read line  144  extending in the Y direction is shared by one column of the pixels  110 . 
     As shown in  FIG. 2 , the pixels  110  are each divided into two, a display system  120  and a sensor system  130 . 
     The display system  120  includes an n-channel transistor  122 , a liquid crystal element  124 , and a storage capacitor  126 . The gate electrode of the transistor  122  connects to the scanning line  112 ; the source electrode connects to the data line  114 ; and the drain electrode connects in common to a first end of the liquid crystal element  124  and a first end of the storage capacitor  126 . A second end of the liquid crystal element  124  connects to a common electrode  128  which is held at a voltage Vcom and connected in common to the pixels  110 . 
     In this embodiment, a second end of the storage capacitor  126  is also connected electrically in common to the common electrode  128 , because it is held at the voltage Vcom. 
     As is known, the liquid crystal element  124  has a structure in which liquid crystal is sandwiched between a pixel electrode connected to the drain electrode of the transistor  122  and the common electrode  128  common to the pixels  110 , so it has a transmittance corresponding to the effective value of the voltage held by the pixel electrode and the common electrode  128 . 
     When the voltage of the scanning line  112  reaches a high level higher than a threshold, the transistor  122  is turned on, so that a voltage provided to the data line  114  is applied to the pixel electrode. Therefore, if the voltage of the data line  114  is brought to a voltage corresponding to the gray level when the scanning line  112  rises to a high level, the difference voltage between the voltage corresponding to the gray level and the voltage Vcom is written to the liquid crystal element  124 . When the scanning line  112  falls to a low level, the transistor  122  is turned off. However, the difference voltage written to the liquid crystal element  124  is held by the voltage holding performance of the liquid crystal element  124  and the storage capacitor  126  connected in parallel thereto, so that the liquid crystal element  124  is given a transmittance corresponding to the held difference voltage. 
     The sensor system  130  includes transistors  131 ,  132 , and  133 , a PIN photodiode  134 , and a sensor capacitor  135 . The transistor  131  is for precharging the sensor capacitor  135  with voltage, of which the gate electrode connects to the control line  142 , the source electrode connects to a feed line for feeding a voltage Pre, and the drain electrode connects to the anode of the photodiode  134 , a first end of the sensor capacitor  135 , and the gate electrode of the transistor  132 . The photodiode  134  and the sensor capacitor  135  are connected in parallel between the drain electrode of the transistor  131  (the gate electrode of the transistor  132 ) and the ground potential Gnd at a reference level. The source electrode of the transistor  132  is grounded to the potential Gnd, and the drain electrode is connected to the source electrode of the reading transistor  133 . The gate electrode of the transistor  133  connects to the control line  143 , and the drain electrode connects to the read line  144 . 
     In the sensor systems  130 , when the control line  142  rises to a high level, the transistor  131  is turned on, so that the sensor capacitor  135  is precharged with the voltage Pre. When the control line  142  falls to a low level, so that the transistor  131  is turned off, a reverse-biased leak current flows through the photodiode  134  as incident light increases, so that the voltage held in the sensor capacitor  135  decreases from the voltage Pre. Specifically, the voltage of a first end of the sensor capacitor  135  substantially is held at the voltage Pre if the leak current of the photodiode  134  is low, and comes close to zero as the leak current increases. 
     When the voltage of the control line  143  is raised to a high level after the read line  144  is precharged with a predetermined voltage, the transistor  133  is turned on, so that the drain electrode of the transistor  132  is connected to the read line  144 . If the quantity of light incident on the photodiode  134  is small, so that the first end of the sensor capacitor  135  is held substantially at the voltage Pre, the transistor  133  is turned on, so that the voltage of the read line  144  sharply changes from the precharge voltage to zero. On the other hand, if the quantity of light incident on the photodiode  134  is large, so that the voltage of the first end of the sensor capacitor  135  drops to zero because of leak current, the transistor  133  is turned off, so that the voltage of the read line  144  changes little from the precharge voltage. 
     In this way, it can be determined whether the quantity of light incident on the pixel  110  at the intersection of the control line  142  ( 143 ) and the read line  144  is large or small according to whether the read line  144  changes from the precharge voltage when the voltage of the control line  142  is decreased from a high level to a low level and then the voltage of the control line  143  is raised to a high level. 
     Although the scanning line  112  and the control lines  142  and  143  of  FIG. 2  are different lines, part of them may be shared. Likewise, although the data line  114 , the read line  144 , and the voltage-Pre feed line are different lines, part of them may be shared. 
     Although one pixel  110  has a set of the display system  120  and the sensor system  130 , the sensor system  130  may be shared by two or more pixels  110 . 
     Referring back to  FIG. 1 , the control circuit  10  controls the Y driver  12 , the X driver  14 , the Y driver  16 , and the read circuit  18 . 
     The Y driver  12  selects one from the scanning lines  112  on the display panel  100  in sequence under the control of the control circuit  10 , and raises the elected scanning line  112  to a high level, with the other scanning lines  112  held at a low level. The X driver  14  applies a voltage corresponding to the gray level of the pixels  110  at the selected scanning line  112  to the data line  114 . 
     The X driver  14  receives an image signal from a higher-level control circuit (not shown), converts it to a voltage suitable for display, and provides it to the data line  114 . For a two-screen display mode, the X driver  14  receives two kinds of image signal. 
     The Y driver  16  executes the operation of lowering the voltage of the control line  142  on the display panel  100  from a high level to a low level, and then raising the voltage of the paired control line  143  to a high level in sequence from one row to another of the pixels  110  under the control of the control circuit  10 . 
     The read circuit  18  serving also as a detection circuit reads the voltages of the precharged read lines  144  of every column, and then determines whether the read voltages have changed from the precharge voltages. Specifically, if the voltage of the read line  144  has changed from the precharge voltage to zero, the read circuit  18  determines that the quantity of light incident on the sensor system  130  of the pixel defined by the column of the read line  144  and the row controlled by the Y driver  16  is large; in contrast, if the voltage of the read line  144  has not changed from the precharge voltage, the read circuit  18  determines that the quantity of light incident on the sensor system  130  of the pixel defined by the column of the read line  144  and the row controlled is small. 
     Thus, by selecting one of the scanning lines  112  in sequence and applying a voltage corresponding to the gray level of the pixel at the selected scanning line  112  to the data line  114 , the liquid crystal element  124  of the display system  120  can hold the voltage corresponding to the gray level. 
     Likewise, by controlling the control lines  142  and  143  one by one and determining changes in the voltages of the read lines  144  every control, the quantity of light incident on the sensor systems  130  can be determined for all the pixels. 
     The time required to control the control lines  142  and  143  from the first to the last rows is referred to as a sensor frame period. In this embodiment, the sensor frame period has no relation to a vertical scanning period required for image display, because the scanning line  112  and the control lines  142  and  143  are independent. 
     The determining circuit  20  stores the results of determination by the sensor systems  130  of all the pixels for several frame periods, from which it determines the operation on the display panel  100  according to the procedure described later. 
       FIG. 3  is a plan view of light-shielding members (image splitters)  150  of the display panel  100  for the matrix pixels  110 , as viewed from the back (from the side opposite to the viewing direction). In this drawing, the driver seat is on the left and the passenger seat is on the right, because it is viewed from the back. 
     As shown in  FIGS. 1 and 3 , the pixels L and the pixels R are arrayed continuously in the vertical direction and alternately in the horizontal direction in a matrix form. As shown in  FIG. 3 , the light-shielding members  150  are each shaped like a belt, which are disposed closer to the viewer than to the liquid crystal element  124  in such a manner that their centers agree with the boundary between the pixels L and the pixels R. The light-shielding members  150  allows the pixels L to open to the driver seat and to be blocked from the light from the passenger seat, and in contrast, allows the pixels R to open to the passenger seat and to be blocked from the light from the driver seat. 
     That is, the light-shielding members  150  common to the display system  120  and the sensor system  130  are provided for each of the pixels L and the pixels R. For the pixels L, for example, the openings of the light-shielding members  150  for the display systems  120  are disposed at the same angle as those of the light-shielding members  150  for the sensor systems  130 . 
     Accordingly, as shown in  FIG. 4 , the display systems  120  of the pixels L are viewed from the driver seat, but the pixels R are blocked; in contrast, the display systems  120  of pixels R are viewed from the passenger seat, but the pixels L are blocked, thus allowing different images to be displayed on the driver seat side and the passenger seat side (two-screen display mode). 
     Also in the sensor systems  130 , the sensor systems  130  of the pixels L are shielded from light from the passenger seat, and the sensor systems  130  of the pixels R are shielded from light from the driver seat. 
     Assuming a driver or passenger seat position, images from the pixels L are concentrated to the driver seat, and images from the pixels R are concentrated to the passenger seat. To this end, the pitches of the pixels L and the pixels R are set slightly larger than that of the openings of the light-shielding members  150 . Referring to  FIG. 4 , the widths of the light-shielding portions of the light-shielding members  150  increase from the center of the display panel  100  to both ends. 
       FIG. 4  shows a simplified arrangement of the light-shielding members  150  for describing the optical paths to the driver seat and the passenger seat. The actual optical paths are shown in  FIG. 3 . 
     The arrangement of the light-shielding members  150  for the array of pixels L and pixels R may be that shown in  FIG. 15 , in addition to that shown in  FIG. 3 . That is, the pixels L and the pixels R may be arrayed alternately row by row, to which the arrangement of the light-shielding members  150  may be changed. This pixel array can improve the resolution of display. 
     The arrangement shown in  FIG. 15  also allows the sensor systems  130  of pixels L to be blocked from light from the passenger seat and the sensor systems  130  of pixels R to be blocked from light from the drive seat. 
     The principle on which the operation on the display panel  100  is detected by this sensor system  130  will be described.  FIG. 6  shows approaches of the operator&#39;s finger, expressed by a sphere, as viewed from above the display panel  100 .  FIGS. 7A and 7B  show changes in the quantity of light with approach. 
     As shown in  FIG. 6 , a finger of the operator sitting in the driver seat may approach the display panel  100  through points (a), (b), and (c) under relatively light outside conditions. In this case, the light that enters the sensor systems  130  of pixels L may be expressed as distribution charts (a), (b), and (c) of  FIG. 7A . That is, the area of the portion with a small quantity of light may be reduced because the area of projection of the finger gradually decreases as the finger approaches the display panel  100 . Here the stroke of the projection center of the finger may be small, because the finger approaches from the driver seat. 
     In contrast, the light that enters the sensor systems  130  of pixels R may be expressed as distribution charts (a), (b), and (c) of  FIG. 7B . Specifically, for a finger at point (a) far from the display panel  100 , the quantity of light that may enter the sensor system  130  of pixels R through the light-shielding members  150  does not change. When the finger reaches point (b), the projection of the finger overlaps with the periphery of the display panel  100  adjacent to the driver seat, so that part of the periphery decreases in light quantity. As the finger approaches point (c), the elliptical projection of the finger moves. 
     When the finger comes into almost contact with the display panel  100 , the parallax between the pixels L and the pixels R becomes almost zero, thus causing overlap between the projection detected in the sensor systems  130  of pixels L and the projection detected in the sensor systems  130  of pixels R. 
     On the other hand, when a finger of the operator sitting in the passenger seat approaches the display panel  100 , the relationship between the pixels L and the pixels R is reversed. 
     Under relatively dark outside conditions such as at night or in a tunnel, light emitted from the backlight (not shown) is reflected by the finger and sensed by the sensor system  130 , so the quantity of light increases conversely as the finger approaches, so that the direction of change of the quantity of light is reversed. However, increases in the area of the portion whose quantity of light changes and shifts of the center of gravity may be the same as those of  FIGS. 6 and 7 . Accordingly, for example, as a finger of the operator sitting in the driver seat approaches the display panel  100 , the area of a small (or large) quantity of light decreases and the shift of the center of gravity thereof is smaller than the amount of approach in the distribution chart of the light incident on the sensor systems  130  of pixels L. 
     The portion with a small or large quantity of light is herein referred to as a light-quantity changed portion for the sake of convenience. 
     The detection mode may be switched according to external environment. For example, the detection result may be reversed between a light ambient condition and a dark ambient condition. 
     Thus, when the distribution of light incident on the sensor systems  130  of pixels R or pixels L changes with time and when the area of the light-quantity changed portion has decreased, with the shift of the center of gravity thereof being small, it can be determined the operation is from the direction corresponding to the pixels at which the changes in quantity of light occurred. Furthermore, when the projection detected by the sensor systems  130  of pixels L and the projection detected by the sensor systems  130  of pixels R overlap and when the area of the overlapped portion has become smaller than a fixed value, it can be determined that a finger has touched the display panel  100 . 
       FIG. 5  is a flowchart showing a concrete procedure of this determination process. 
     After the determining circuit  20  obtains the results of detection of all the pixels of the sensor systems  130 , it stores the detection results for comparison in step Sa 1  of the next time, reads the results of detection obtained one sensor frame period before, and compares them with the detection results of this time to determine whether or not the shape of the portion with a small or large quantity of light (light-quantity changed portion) has changed in the sensor systems  130  of pixels L or pixels R. In the case where step Sa 1  is executed for the first time, no detection result of one sensor frame period before is stored, so that the determination is executed after detection results of one sensor frame have been stored. 
     If it is determined that there is no change (No) the procedure returns to step Sa 1 , wherein the determining circuit  20  stands by for the next determination after a lapse of one sensor frame period. On the other hand, if it is determined that there is a change (Yes), the procedure moves to step Sa 2 . 
     The timing to execute step Sa 1  is the time when the results of detection of the sensor systems  130  are obtained for all the pixels. Accordingly, step Sa 1  of this embodiment is executed at the cycle of the sensor frame period. 
     In step Sa 2 , the determining circuit  20  determines whether the area of the light-quantity changed portion of the sensor systems  130  of pixels L or pixels R has decreased and whether the shift of the center of gravity of the light-quantity changed portion is within a threshold. 
     For example, when the finger approaches to the display panel  100  from the driver seat, the results of detection on the sensor systems  130  of pixels L shows that the area of the light-quantity changed portion is reduced; in contrast, the results of detection on the sensor systems  130  of pixels R shows that the area of the light-quantity changed portion is increased. However, in this case, the shift of the center of gravity of the light-quantity changed portion sensed from the sensor systems  130  of pixels L is small. 
     Thus, the determining circuit  20  can determine that the finger approaches to the display panel  100  from the driver seat from the results that the area of the light-quantity changed portion is reduced and that the shift of the center of gravity of the light-quantity changed portion is within a threshold. In the case where the finger approaches to the display panel  100  from the passenger seat, the relationship between pixels L and pixels R is reversed. However, the reduction in the area of the light-quantity changed portion and the small shift of the center of gravity are the same. 
     If the determination in step Sa 2  is “No”, the procedure returns to step Sa 1 . 
     If the determination in step Sa 2  is “Yes”, then the determining circuit  20  determines whether the outside diameter of the light-quantity changed portion has become smaller than a threshold (step Sa 3 ). For example, in the case where the finger approaches to the display panel  100  from the driver seat, if the outside diameter of the light-quantity changed portion is larger than a threshold the results of detection on the sensor systems  130  of pixels L show that the finger approaches the display panel  100  but is far from the display panel  100  to some extent. In this state, the determination of step Sa 3  is “No”, and the procedure returns to step Sa 1 . 
     In contrast, the determination in step Sa 3  is “Yes”, the determining circuit  20  determines whether or not the reduction in the area of the light-quantity changed portion and the shift of the center of gravity smaller than a threshold have occurred in the sensor systems  130  of pixels L (step Sa 4 ). 
     If the determination in step Sa 4  is “Yes”, then the determining circuit  20  determines that the person sitting in the driver seat has touched the display panel  100  with a finger (step Sa 5 ); if the determination is “No”, then the determining circuit  20  determines that the person sitting in the passenger seat has touched the display panel  100  (step Sa 6 ). After the determination in step Sa 5  or Sa 6 , the determining circuit  20  sends the determination to a higher-level control circuit of the car navigation system. Thus, a process corresponding to the touch operation is executed. 
     Examples of the process corresponding to the touch operation are switching the display screen in the direction of the touch operation and controlling the video or radio. 
     After the process of step Sa 5  or Sa 6 , the procedure returns to step Sa 1 , where the determining circuit  20  stands by for the next determination after a lapse of a sensor frame period. Every time the results of determination on all the pixels of the sensor systems  130  are obtained, the determining circuit  20  repeats the process of steps Sa 1  to Sa 6 . 
     If the person sitting in the driver seat or the passenger seat moves a finger or the like toward the display panel  100 , both of the determinations in steps Sa 1  and Sa 2  result in “Yes”. If the finger or the like comes into almost contact with the display panel  100 , the determination in step Sa 3  results in “Yes”, and a determination is made whether or not the approach is from the driver seat (step Sa 4 ). 
     If there is no action, the determination in step Sa 1  results in “No”; if there is an action but it is not an approach to the display panel  100 , the determination in step Sa 2  results in “No. If there is an approach but a finger or the like has not come to almost contact with the display panel  100 , the determination in step Sa 3  results in “No”. 
     Thus, this embodiment allows direct determination on the direction of approach of the finger or the like from the temporal changes of the light-quantity changed portion of the sensor systems  130  of pixels L or pixels R. Therefore, even if icons are displayed on substantially the same position on the display screen by pixels L for the driver seat and the display screen by pixels R for the passenger seat, this embodiment allows determination whether the touch operation is made from the driver seat or the passenger seat. 
     Application and Modification of First Embodiment 
     In the case where a finger or the like approaches from the driver seat, for example, the procedure of the flowchart of  FIG. 5  does not give consideration to changes of the light-quantity changed portion of the sensor systems  130  of pixels R. However, as described with reference to  FIGS. 6 and 7 , in the state in which a finger or the like approaches from the driver seat or the passenger seat so that the centers of gravity of the light-quantity changed portions of the sensor systems  130  of pixels L and pixels R agree with each other and the finger comes into contact with the display panel  100 , effects of parallax due to the light-shielding members  150  are eliminated. Accordingly, the shapes and the centers of gravity of the light-quantity changed portions of the sensor systems  130  of pixels L and pixels R agree substantially. 
     Thus, the touch operation should be determined by comparing the shapes and the centers of gravity of the light-quantity changed portions of the sensor systems  130  of pixels L and pixels R. 
       FIG. 8  is a flowchart for the procedure of determining the approach and the touch operation. Steps Sb 1 , Sb 5 , and Sb 6  of this flowchart are the same as steps Sa 1 , Sa 5 , and Sa 6  of  FIG. 5 , respectively. 
     After the determining circuit  20  obtains the results of detection of all the pixels of the sensor systems  130 , it compares the detection results with the results of detection obtained one sensor frame period before to determine whether or not the shape of the light-quantity changed portion has changed in the sensor systems  130  of pixels L or pixels R. If it is determined that there is no change (No), the procedure returns to step Sb 1 . On the other hand, if it is determined that there is a change (Yes), the procedure moves to step Sb 2 , wherein the determining circuit  20  finds the centers of gravities of the light-quantity changed portions of the sensor systems  130  of pixels L and pixels R, and determines whether or not the distance between them is within a threshold. 
     If the distance is not within the threshold (No) the procedure returns to step Sb 1 ; if the distance is within the threshold (Yes), the determining circuit  20  determines whether or not the shift of the center of gravity of the light-quantity changed portion in the sensor systems  130  of pixels L is smaller than that of the pixels R. 
     If the determination in step Sb 3  is “Yes”, then the determining circuit  20  determines that the person sitting in the driver seat has touched the display panel  100  with a finger (step Sb 5 ); if the determination is “No”, then the determining circuit  20  determines that the person sitting in the passenger seat has touched the display panel  100  (step Sb 6 ). After the determination in step Sb 5  or Sb 6 , the procedure returns to step Sb 1 , where the determining circuit  20  stands by for the next determination after a lapse of one sensor frame period. 
     This method also allows determination whether the touch operation is made from the driver seat or the passenger seat. 
     Second Embodiment 
     A display device according to a second embodiment of the invention will next be described. 
       FIG. 9  shows the structure of a display device  1  according to the second embodiment. The display device  1  of the second embodiment is the display of a car navigation system, as in the first embodiment. The difference from the first embodiment is that the determination by the determining circuit  20  is fed back to the control circuit  10 , with which the control circuit  10  controls the Y driver  16  for driving the sensor systems  130  and the read circuit  18 . The second embodiment will therefore be described mainly on the difference, that is, the control process. 
     Referring to  FIG. 11 , for example, when a finger of the operator sitting in the driver seat has reached point (1) halfway to the display panel  100 , light incident on the part of the passenger-seat-side pixels R closest to the driver seat is blocked by the finger. In contrast, when a finger of the operator sitting in the passenger seat has reached point (2) halfway to the display panel  100 , light incident on the part of the driver-seat-side pixels L closest to the passenger seat is blocked by the finger. 
     In other words, when a finger or the like approaches from one of the driver seat and the passenger seat, the outermost part of the sensor systems of the other of the driver seat side and the passenger seat side changes in light quantity. 
     This eliminates the need for using all the sensor systems  130  for detection, allowing only the outermost sensor systems  130  on the outermost vertical two sides of the matrix array, or more specifically, only the pixels L and pixels R indicated by symbol * in  FIG. 11 . Thus, when one of the sensor systems  130  of pixels L and pixels R changes in light quantity, the other of the sensor systems  130  is operated to detect the touch operation, so that the power to be consumed by the operation of the sensor systems  130  can be reduced. 
       FIG. 10  is a flowchart showing a concrete procedure of this process. 
     First in step Sc 1 , the determining circuit  20  instructs the control circuit  10  to operate only the pixels L and pixels R of the sensor systems  130  on the outermost vertical two sides of the matrix array. Accordingly, the control circuit  10  controls the read circuit  18  so that it operates only four columns of read lines  144  in total including the left two columns and the right two columns and does not operate the other read lines  144 , without changing the control on the Y driver  16 . 
     Next, after obtaining the results of detection on the sensor systems  130  of pixels L and pixels R on the outermost vertical two sides, the determining circuit  20  compares the results with those obtained one sensor frame period before to determine whether a light-quantity changed portion has occurred in either of the sensor systems  130 . 
     If it is determined that there is no change (No) the procedure returns to step Sc 2 , wherein the determining circuit  20  stands by for the next determination after a lapse of one sensor frame period. Thus, as long as the result of determination in step Sc 2  is “No”, only the pixels L and pixels R on the outermost vertical two sides of the matrix array are operated in the sensor systems  130 . 
     On the other hand, if it is determined that there is a change (Yes), the procedure moves to step Sc 3 , wherein the determining circuit  20  determines whether the light-quantity changed portion has occurred in the sensor systems  130  of pixels R. 
     If the determination is “Yes”, which indicates that this approach is from the driver seat, then the determining circuit  20  instructs the control circuit  10  to operate only the sensor systems  130  of pixels L (step Sc 4 ). Thus, the control circuit  10  controls the read circuit  18  so that it operates only the read lines  144  of the columns of pixels L and does not operate the read lines  144  of the columns of pixels R. 
     On the other hand, if the determination in step Sc 3  is “No”, which indicates that the light-quantity changed portion is generated in the sensor systems  130  of pixels L, indicating the approach is from the passenger seat, the determining circuit  20  instructs the control circuit  10  to operate only the sensor systems  130  of pixels R (step Sc 5 ). Thus, the control circuit  10  controls the read circuit  18  so that it operates only the read lines  144  of the columns of pixels R and does operate the read lines  144  of the columns of pixels L. 
     After the determining circuit  20  has obtained all the results of detection on the sensor systems  130  of pixels L or pixels R after step Sc 4  or Sc 5 , the determining circuit  20  compares, in step Sc 11 , the results with those obtained one sensor frame period before to determine whether or not the shape of the light-quantity changed portion has changed. In the case where step Sc 11  is executed for the first time, there is no stored detection result of one sensor frame period before, so that the determination is executed after detection results of one sensor frame have been stored. 
     If it is determined in step Sc 11  that there is no change (No), the procedure returns to step Sc 11 , wherein the determining circuit  20  stands by for the next determination after a lapse of one sensor frame period. On the other hand, if it is determined that there is a change (Yes), the determining circuit  20  determines in step Sc 12  whether the change is a decrease in the area of the light-quantity changed portion and whether the shift of the center of gravity of the light-quantity changed portion is within a threshold. 
     If the determination is “No”, the procedure returns to step Sc 11 ; on the other hand, if the determination is “Yes”, then the determining circuit  20  determines whether the outside diameter of the light-quantity changed portion is smaller than a threshold (step Sc 13 ). 
     If the determination in step Sc 13  is “No”, the procedure returns to step Sc 11 ; on the other hand, if the determination is “Yes”, the determining circuit  20  determines whether the change occurs in the pixels L of the sensor systems  130  in operation (step Sc 14 ). If the determination in step Sc 14  is “Yes”, then the determining circuit  20  determines that the person sitting in the driver seat has touched the display panel  100  with a finger (step Sc 15 ); if the determination is “No”, then the determining circuit  20  determines that the person sitting in the passenger seat has touched the display panel  100  (step Sc 16 ). 
     After step Sc 15  or Sc 16 , the procedure returns to step Sc 1 , and the processes of steps Sc 1  to Sc 5  and Sc 11  to Sc 16  are repeated. 
     In this embodiment, in the initial state of detection, only the sensor systems  130  of pixels L and pixels R on the outermost vertical two sides of the matrix array are operated. When the person sitting in the driver seat or the passenger seat moves a finger or the like toward the display panel  100 , only all of one of the pixels L and pixels R corresponding to the direction of approach are operated according to the determinations in step Sc 2  and Sc 3 . Accordingly, in this embodiment, only the sensor systems  130  of pixels L and pixels R on the outermost vertical two sides have to be operated as long as the determination in step Sc 2  is “No”. Even if the determination in step Sc 2  turns to “Yes”, only one of the sensor systems  130  of Pixels L and pixels R has to be operated, so that the power required to operate the sensor systems  130  can be reduced. 
     Third Embodiment 
     Although the first and second embodiments are configured to detect the direction of approach of a finger or the like for the driver seat side and the passenger seat side, the third embodiment is configured to detect an approach from the rear seat (central rear seat). 
     Since the structure of the third embodiment is the same as that of the first embodiment (see  FIG. 1 ), the description is concentrated to the principle and procedure of detection. 
     As shown in  FIG. 13 , when a finger of the operator sitting in the rear seat approaches from the front of the display panel  100 , the finger may pass through points (a) and (b). 
     When the finger reaches point (a), for the sensor systems  130  of pixels L, the pixels L adjacent to the passenger seat change in light quantity, as shown in (a) of  FIG. 14A ; for the sensor systems  130  of pixels R, the pixels R adjacent to the driver seat change in light quantity, as shown in (a) of  FIG. 14B . 
     When the finger reaches point (b), for the sensor systems  130  of pixels L, the center of the elliptical projection of the finger moves toward the portion to be touched in the direction of the driver seat, as shown in (b) of  FIG. 14A ; in contrast, for the sensor systems  130  of pixels R, the center of the elliptical projection of the finger moves toward the portion to be touched in the direction of the passenger seat, as shown in (b) of  FIG. 14B . 
     Accordingly, in the case of touch operation from the rear seat, the light-quantity changed portions detected by the sensor systems  130  of pixels L and pixels R become substantially symmetrical about the portion to be touched. Thus, the determining circuit  20  can determine that the touch operation is from the rear seat by detecting that the light-quantity changed portions are symmetrical. 
       FIG. 12  is a flowchart showing a concrete procedure of this process. 
     After obtaining the results of detection of all the pixels of the sensor system  130 , in step Sd 1 , the determining circuit  20  compares them with the detection results obtained one sensor frame period before to determine whether or not the shape of the light-quantity changed portion has changed in the sensor system  130  of pixels L or pixels R. 
     If it is determined that there is no change (No) the procedure returns to step Sd 1 , wherein the determining circuit  20  stands by for the next determination after a lapse of one sensor frame period. On the other hand, if it is determined that there is a change (Yes), the determining circuit  20  determines in step Sd 2  whether the area of the light-quantity changed portion of the sensor system  130  of pixels L or pixels R has reduced and whether the shift of the center of gravity of the light-quantity changed portion is within a threshold. 
     If the determination in step Sd 2  is “Yes”, the determining circuit  20  executes the process of steps Sd 3  to Sd 6  similar to step Sc 3  to Sc 6  of the first embodiment to determine whether the touch operation is from the driver seat or the passenger seat. 
     If the determination in step Sd 2  is “No”, the determining circuit  20  determines in step Sd 11  whether the light-quantity changed portions by the sensor systems  130  of the pixels L and pixels R are in symmetry. 
     If the determination is “No”, the procedure returns to step Sd 1 ; if the determination is “Yes”, the determining circuit  20  finds the centers of gravities of the light-quantity changed portions by the sensor systems  130  of pixels L and pixels R, and determines whether the distance between the centers is within a threshold (step Sd 12 ). If the distance is not within the threshold (No), the procedure returns to step Sd 1 . If the distance is within the threshold (Yes), the determining circuit  20  determines in step Sd 13  that the approach of the finger or the like is from the rear seat and that the finger or the like has touched the display panel  100 , and sends the determination to the control circuit  10  or a higher-level control circuit of the car navigation system. 
     The control circuit  10  of the third embodiment controls the screen as follows in response to the touch operation: 
     The control circuit  10  controls the display of the display panel  100  in such a manner that if only a touch operation from the driver seat is detected and no touch operation from the passenger seat or the rear seat is detected for a fixed period, the display is put into a one-screen mode in which only the screen for the driver seat is displayed and if a touch operation from the driver seat or the rear seat is added for a fixed period, the display is put into a two-screen mode in which both the screen for the driver seat and the screen for the passenger seat are displayed. 
     Another example of screen control is that described in the first embodiment. 
     After the process of steps Sd 5  and Sd 6  or step Sd 13 , the procedure returns to step Sd 1 , wherein the determining circuit  20  stands by for the next determination after a lapse of one sensor frame period. 
     In this way, the third embodiment allows direct determination whether a finger touch operation is made from the rear seat, in addition to those from the driver seat and the passenger seat. 
     Although the above embodiments are configured to determine that a touch operation is made when a finger or the like has touched the display panel  100 , the determination may be made when it has reached close proximity to some extent, and in other words, it has approached from any direction. 
     Although the above embodiments describe the display panel  100  as a liquid crystal display, other display devices such as an organic electroluminescence display device and a plasma display device that combine the sensor systems  130  in the pixels can also detect an approaching direction and touch operation. 
     In addition to the car navigation system described above, examples of electronic devices incorporating the display device include devices that require touch operation such as portable phones, digital still cameras, televisions, viewfinder or monitor-direct-view type videotape recorders, pagers, electronic notebooks, calculators, word processors, workstations, TV phones, and POS terminals. 
     The entire disclosure of Japanese Patent Application No. 2007-110454, filed Apr. 19, 2007 is expressly incorporated by reference herein.