Abstract:
Devices, methods, and non-transitory computer-readable media consistent with the invention may be used to detect an area of contact on a surface of the device by an external object. Then, an inclination of the device may be determined based on the detected area of contact.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    This invention relates to an information processing apparatus, an inclination detection method and an inclination detection program and can be suitably applied, for example, to an information processing apparatus which has a touch panel. 
         [0003]    2. Description of the Related Art 
         [0004]    In recent years, an information processing apparatus like an information processing apparatus  1  shown in  FIG. 1  wherein an instruction can be applied in various applications of games and so forth by a user inclining a housing of the information processing apparatus  1  has popularized. 
         [0005]    As one of such information processing apparatus like the information processing apparatus  1 , an information processing apparatus is disclosed, for example, in Japanese Patent Laid-Open No. 2002-207567 (referred to as Patent Document 1 hereinafter). In the information processing apparatus disclosed in Patent Document 1 mentioned, a sensor which detects force acting upon a physical solid to detect an inclination of a housing such as an acceleration sensor or a gyro sensor is used to detect the inclination of the housing, and various processes are carried out in response to the detected inclination. It is to be noted that the sensor of the type described is hereinafter referred to also as inclination detection sensor. 
         [0006]    Incidentally, the information processing apparatus of Patent Document 1 described above cannot detect the inclination of the housing without using an inclination detection sensor. 
       SUMMARY 
       [0007]    Disclosed is an information processing apparatus, an inclination detection method and an inclination detection program wherein the inclination of a housing can be detected without using an inclination detection sensor. 
         [0008]    Consistent with one embodiment, an apparatus for use in an inclinable device. The device may include a detector for determining an area of contact on a surface of the device by an object external to the device; a memory storing instructions for determining a change in inclination of the device, based on the area of contact; and one or more processors for executing the instructions. 
         [0009]    Consistent with another embodiment a method for detecting a change in inclination of a device is disclosed. The method may include determining an area of contact on a surface of the device by an object external to the device; and determining the change in the inclination of the device based on the area of contact. 
         [0010]    Consistent with another embodiment, there is provided a non-transitory computer-readable medium storing a set of instructions which, when executed by a processor, performs a method. The method may include determining an area of contact on a surface of a device by an object external to the device; and determining a change in the inclination of the device based on the area of contact. 
         [0011]    In the information processing apparatus, when a user grasps the housing, the angle of a finger, which contacts the predetermined face of the housing, on the predetermined face can be detected. Then, since the angle varies as the housing is inclined, the inclination of the housing can be detected based on the variation of the angle. 
         [0012]    With the information processing apparatus, when a user grasps the housing, the angle of the finger, which contacts the predetermined face of the housing, on the predetermined face can be detected. Then, since this angle varies as the housing is inclined, the inclination of the housing can be detected based on the variation of the angle. Thus, an information processing apparatus, an inclination detection method and an inclination detection program wherein the angle of the housing can be detected without using an inclination detection sensor can be implemented. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic view illustrating an example of use of an information processing apparatus in the related art; 
           [0014]      FIGS. 2A and 2B  are a schematic perspective view and a block diagram showing an appearance and a general configuration of an information processing apparatus to which the present invention is applied, respectively; 
           [0015]      FIGS. 3A and 3B  are schematic front elevational views of the information processing apparatus of  FIGS. 2A and 2B  illustrating detection of an angle of a contacting physical solid; 
           [0016]      FIGS. 4A to 4F  are schematic front elevational views illustrating an inclination detection process consistent with a first embodiment; 
           [0017]      FIGS. 5A and 5B  are schematic front elevational views of the information processing apparatus of  FIGS. 2A and 2B  illustrating adjustment of the sound volume; 
           [0018]      FIGS. 6A and 6B  are schematic front elevational views of the information processing apparatus of  FIGS. 2A and 2B  illustrating changeover of an album to be selected; 
           [0019]      FIGS. 7A and 7B  are schematic front elevational views of the information processing apparatus of  FIGS. 2A and 2B  illustrating fast forward feeding or fast reverse feeding of dynamic pictures; 
           [0020]      FIGS. 8A and 8B  are schematic front elevational views of the information processing apparatus of  FIGS. 2A and 2B  illustrating scrolling of images; 
           [0021]      FIG. 9  is a flow chart illustrating an inclination detection processing procedure according to the first embodiment; 
           [0022]      FIG. 10  is a block diagram showing a functional configuration of the information processing apparatus of  FIGS. 2A and 2B ; 
           [0023]      FIGS. 11A to 11F  are schematic front elevational views of the information processing apparatus of  FIGS. 2A  and  2 B illustrating an inclination detection process according to a second embodiment; and 
           [0024]      FIG. 12  is a flow chart illustrating an inclination detection processing procedure according to the second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0025]    In the following, embodiments consistent with the invention are described. It is to be noted that the description is given in the following order. 
         [0026]    1. First Embodiment (example wherein the inclination of the housing is detected where the housing is grasped by both hands) 
         [0027]    2. Second Embodiment (example wherein the inclination of the housing is detected where the housing is grasped by one hand) 
         [0028]    3. Other Embodiments 
       1. First Embodiment 
     1-1. General Configuration of the Information Processing Apparatus 
       [0029]    First, the first embodiment is described. 
         [0030]    Referring to  FIGS. 2A and 2B , the information processing apparatus is generally denoted by reference numeral  10 . The information processing apparatus  10  is of the portable type and has a housing  11  of a flattened rectangular shape of such a size that it can be grasped by one hand as seen in  FIG. 2A , that is, of a palm size. 
         [0031]    A touch panel  12  in the form of a rectangular plate is provided on the surface of the housing  11 . The touch panel  12  is of the optical sensor type and includes a display section  12 A and an optical sensor  12 B. If the information processing apparatus  10  recognizes an operation of a user on a display face of the touch panel  12  thereof, then it carries out various processes in response to the operation. 
         [0032]    It is to be noted that, since the housing  11  and the touch panel  12  are formed shorter in a first direction than in a second direction, the first direction is hereinafter referred to as lateral direction. Further, since the housing  11  and the touch panel  12  are formed longer in the second direction than in the first direction, the second direction is hereinafter referred to as longitudinal direction. 
         [0033]    The information processing apparatus  10  is designed such that it is normally used in a horizontal posture in which the longitudinal direction of the information processing apparatus  10  coincides with the leftward and rightward direction by its user. Meanwhile, the direction of the information processing apparatus  10  where it is used in another posture wherein the longitudinal direction thereof coincides with the upward and downward direction is hereinafter referred to also as vertical direction. 
         [0034]    A headphone terminal not shown is provided on a left face of the housing  11  such that a headphone  13  is connected to the housing  11  through the headphone terminal. The information processing apparatus  10  allows the user to enjoy sound of a reproduced musical composition or dynamic picture through the headphone  13 . 
         [0035]    Now, circuit components of the information processing apparatus  10  are described with reference to  FIG. 2B . The information processing apparatus  10  includes several components connected to each other by a bus  20 . A CPU (Central Processing Unit)  21  reads out a program stored in a nonvolatile memory  22  into a RAM (Random Access Memory)  23 . Then, the CPU  21  develops the read out program on the RAM  23  and controls the other circuit components and executes various processes in accordance with the read out program. 
         [0036]    If the CPU  21  is connected to an external apparatus through an external connection terminal not shown, then it can acquire music data, dynamic picture data or image data from the external apparatus and store the acquired data into the nonvolatile memory  22 . 
         [0037]    If the CPU  21  receives an instruction to reproduce a musical composition through a user operation, then it reads out the music data stored in the nonvolatile memory  22 . Then, the CPU  21  carries out predetermined reproduction processes such as a decoding process and an amplification process for the music data to obtain a sound signal and sends the sound signal to a sound outputting section  24 . Sound of the musical composition based on the sound signal is outputted from the sound outputting section  24  through the headphone  13 . 
         [0038]    A plurality of pixel sets are disposed, for example, in a matrix on a display face of the touch panel  12 . Each of the pixel sets includes a display section  12 A including light emitting elements for red display, green display and blue display, and an optical sensor  12 B. 
         [0039]    The CPU  21  causes the display sections  12 A to display various menu screens and an image based on image data. For example, the CPU  21  reads out jacket photograph image data annexed to the music data stored in the nonvolatile memory  22  and causes the display sections  12 A to display a jacket photograph image based on the jacket photograph image data. 
         [0040]    The optical sensors  12 B receive light incident to the display face of the touch panel  12 , produce light intensity signals corresponding to intensities of the received light at predetermined intervals and send the light intensity signals to the CPU  21 . 
         [0041]    Here, it is assumed that the housing  11  is grasped by a hand such that a finger of the user touches the display face of the touch panel  12  as seen in  FIG. 3A . In this instance, it can be estimated that the ball of the fingertip contacts the display face of the touch panel  12  and the other portion than the ball of the fingertip does not contact with the display face but is positioned in the proximity of the display face. 
         [0042]    In this instance, in the region in which the finger of the user contacts the display face of the touch panel  12 , since light directed to the display face is intercepted by the finger of the user, the intensity of light received by the optical sensors  12 B decreases. 
         [0043]    Meanwhile, in the region in which the finger of the user is positioned in the proximity of the display face of the touch panel  12 , since a shadow of the finger of the user is formed, the intensity of light received by the optical sensors  12 B decreases a little. However, the intensity of light is higher than that in the region in which the finger contacts the display face. 
         [0044]    On the other hand, in a region in which the finger of the user does not contact nor is positioned in the proximity of the display face of the touch panel  12 , light to be incident to the display face is not intercepted. Therefore, the intensity of light received by the optical sensors  12 B in the region is higher than that in the region in which the finger contacts or is positioned in the proximity of the display face. 
         [0045]    Taking this into consideration, the CPU  21  carries out a ternary coding process for the light intensity on the pixel sets based on the light intensity signals sent from the optical sensor  12 B at the predetermined distances. The ternary coding process uses two predetermined threshold values set therefor, and the light intensities having various distributions are coded into three values of “−1,” “0” and “1” with reference to the threshold values. 
         [0046]    It is to be noted that the threshold values are set in advance so that the intensity of light in the region in which the finger contacts the display face of the touch panel  12  indicates “−1” while the light intensity in the region in which the finger is positioned in the proximity with the display face indicates “0” and the light intensity in the region in which the finger neither contacts nor is positioned in the proximity of the display face indicates “1.” 
         [0047]    The CPU  21  detects a region in which the light intensity is “−1” on the display face of the touch panel  12 , that is, a dark region Bk, as coordinates on the display face as seen in  FIG. 3B  based on a result of the ternary coding process. 
         [0048]    When the CPU  21  detects the dark region Bk, it recognizes that a physical solid, here, a finger of the user, contacts the display face of the touch panel  12 . It is to be noted that the physical solid contacting the display face of the touch panel  12  as recognized by the CPU  21  is hereinafter referred to as contacting physical solid. 
         [0049]    Then, the CPU  21  recognizes the shape of the dark region Bk as a shape of the portion at which the contacting physical solid contacts the display face of the touch panel  12 . The CPU  21  can thereby recognize the shape of the ball of the fingertip of the finger which contacts the display face. 
         [0050]    Further, the CPU  21  detects a region in which the light intensity on the display face of the touch panel  12  is “0,” that is, an intermediate region Bm, as coordinates on the display screen based on a result of the ternary coding process. 
         [0051]    If the CPU  21  detects the intermediate region Bm together with the dark region Bk, then it recognizes the shape of the intermediate region Bm as a shape of a portion at which the contacting physical solid is positioned in the proximity of the display face of the touch panel  12 . Consequently, the CPU  21  can recognize the shape of a portion other than the ball of the fingertip of the finger which contacts the display face. 
         [0052]    Furthermore, the CPU  21  detects a region in which the light intensity is “1” on the display face of the touch panel  12 , that is, a bright region Br, as coordinates on the display face based on a result of the ternary coding process. The CPU  21  recognizes the bright region Br as a region in which the physical solid neither contacts nor is positioned in the proximity of the display face. 
         [0053]    Then, the CPU  21  detects the center Kp of gravity (i.e., centroid) of the dark region Bk and the center Mp of gravity of the intermediate region Bm as coordinates on the display face of the touch panel  12  based on the coordinates of the dark region Bk and the intermediate region Bm. 
         [0054]    Incidentally, the center Kp of gravity of the dark region Bk is positioned rather near to the fingertip side of the finger which contacts the display face of the touch panel  12  than the center Mp of gravity of the intermediate region Bm, and the center Mp of gravity of the intermediate region Bm is positioned rather near to a root portion of the finger than the center Kp of gravity of the dark region Bk. 
         [0055]    Taking this into consideration, the CPU  21  calculates an angle defined by a direction in which the center Kp of gravity of the dark region Bk is positioned with respect to the center Mp of gravity of the intermediate region Bm and the longitudinal direction of the touch panel  12  as an angle α of the contacting physical solid on the display face of the touch panel  12 . 
         [0056]    Consequently, the CPU  21  can detect the angle defined by the direction in which the fingertip is positioned with respect to the root of the finger and the longitudinal direction on the display face of the touch panel  12  and can detect the angle of the finger which contacts the display face on the display face. 
         [0057]    It is to be noted that the CPU  21  determines that, in a condition wherein the direction in which the center Kp of gravity is positioned with respect to the center Mp of gravity is a parallel direction to the longitudinal direction of the touch panel  12  and the center Kp of gravity is positioned on the right side with respect to the center Mp of gravity, the angle α of the contacting physical solid is zero degree, and the direction in which the center Kp of gravity moves in the counterclockwise direction is a positive direction. For example, the CPU  21  calculates that, in a state wherein the center Kp of gravity is just above the center Mp of gravity, the angle α of the contacting physical solid is 90 degrees. 
       1-2. Inclination Detection Process 
       [0058]    Now, an inclination detection process for detecting the inclination β ( FIG. 4 ) of the housing  11  of the information processing apparatus  10  is described in detail. 
         [0059]    The information processing apparatus  10  has an inclination detection mode in which the user can input a command by inclining the housing  11 . If an operation of contacting left and right fingers with the display face of the touch panel  12  is carried out by the user, then the information processing apparatus  10  changes over the operation mode thereof into the inclination detection mode. 
         [0060]    Here, it is assumed that the user carries out an operation for changing over the operation mode of the information processing apparatus  10  to the inclination detection mode. In other words, it is assumed that the user grasps the housing  11  in a horizontally directed state and contacts the display face of the touch panel  12  at left and right fingers as seen in  FIG. 4A . 
         [0061]    At this time, the CPU  21  carries out the ternary coding process described above based on the intensities of light received by the optical sensors  12 B and detects a dark region Bk and an intermediate region Bm on the display face of the touch panel  12  as seen in  FIG. 4B . Here, since the left and right fingers of the user contact the display face, two dark regions Bk and two intermediate regions Bm are detected. 
         [0062]    The CPU  21  detects the center Kp of gravity of each of the dark regions Bk and decides whether or not one center Kp of gravity is found in each of a right region and a left region of the display face of the touch panel  12  into which the display face is divided with respect to the center O thereof. 
         [0063]    If the CPU  21  decides that one center Kp of gravity is found in each of the right region and the left region of the display face of the touch panel  12 , then it recognizes that a physical solid contacts each of the left and right sides of the display face. 
         [0064]    It is to be noted that, in the following description, the center Kp of gravity of the left region of the display face of the touch panel  12  is referred to also as center KpL of gravity, and the dark region Bk, intermediate region Bm and center Mp of gravity of the intermediate region Bm corresponding to the center KpL of gravity are referred to also as dark region BkL, intermediate region BmL and center MpL of gravity, respectively. Meanwhile, the center Kp of gravity of the right region of the display screen is referred to also as center KpR of gravity, and the dark region Bk, intermediate region Bm and center Mp of gravity of the intermediate region Bm corresponding to the center KpR of gravity are referred to also as dark region BkR, intermediate region BmR and center MpR of gravity, respectively. 
         [0065]    Further, in the following description, a physical solid which contacts the left region of the display face of the touch panel  12  is referred to also as left region contacting physical solid, and a physical solid which contacts the right region of the display face of the touch panel  12  is referred to also as right region contacting physical solid. 
         [0066]    If the CPU  21  recognizes that a physical solid contacts each of the opposite left and right regions of the display face of the touch panel  12 , then it recognizes that an operation for changing over the operation mode to the inclination detection mode has been carried out and changes over the operation mode of the information processing apparatus  10  to the inclination detection mode. 
         [0067]    Then, the CPU  21  detects the center MpL of gravity of the intermediate region BmL and the center MpR of gravity of the intermediate region BmR. 
         [0068]    Then, the CPU  21  calculates the angle αL of the left region contacting physical solid on the display face of the touch panel  12  based on the center KpL of gravity of the dark region BkL and the center MpL of gravity of the intermediate region BmL. Further, the CPU  21  calculates the angle αR of the right region conducting physical solid on the display face of the touch panel  12  based on the center KpR of gravity of the dark region BkR and the center MpR of gravity of the intermediate region BmR. 
         [0069]    Consequently, the CPU  21  can detect the angles of the left finger and the angle of the right finger which currently contact the display face of the touch panel  12 . 
         [0070]    Incidentally, if the operation for changing over the operation mode of the information processing apparatus  10  to the inclination detection mode is carried out, then the CPU  21  recognizes that the user is going to incline the housing  11  and recognizes that the state at this point of time is a state wherein the housing  11  is not inclined, that is, a state wherein the inclination of the housing  11  is zero degree. 
         [0071]    Therefore, the CPU  21  sets the angle αL of the left region contacting physical solid and the angle αR of the right region contacting physical solid at this time as a left region starting angle and a right region starting angle which are angles of contacting solids, respectively, when the operation of inclining the housing  11  is started. It is to be noted that the left region starting angle and the right region starting angle are collectively referred to as starting angles. 
         [0072]    Further, the CPU  21  sets the center KpL of gravity of the dark region BkL and the center KpR of gravity of the dark region BkR at this time as a left finger starting gravity center and a right finger starting gravity center, respectively, when the operation of inclining the housing  11  is started. It is to be noted that the left finger starting gravity center and the right finger starting gravity center are collectively referred to also as starting gravity centers. In other words, the CPU  21  sets the center of gravity of a region in which the contacting physical solid which contacts the display face of the touch panel  12  in a state wherein the housing  11  is not inclined. 
         [0073]    Here, it is assumed that the user inclines the housing  11 , for example, in the clockwise direction as seen in  FIG. 4C  from a state wherein the user carries out an operation for changing over the operation mode of the information processing apparatus  10  to the inclination detection mode illustrated in  FIG. 4A . When the user inclines the housing  11 , it may possibly vary the angles of the left and right fingers around the centers of gravity of the fingertips of the left and right fingers, that is, of the portions of the fingertips contacting the display face of the touch panel  12  to incline the housing  11 . 
         [0074]    Taking this into consideration, the CPU  21  decides whether or not the angle α of each contacting physical solid has varied from its starting angle. 
         [0075]    In particular, the CPU  21  carries out the ternary coding process based on the intensities of light received by the optical sensors  12 B to detect the dark regions BkL and BkR and the intermediate regions BmL and BmR on the display face of the touch panel  12  as seen in  FIG. 4D . 
         [0076]    Then, the CPU  21  calculates the angle αL of the left region contacting physical solid and the angle αR of the left region contacting physical solid as described hereinabove. 
         [0077]    Then, the CPU  21  calculates the difference dL between the left region starting angle and the angle αL of the left region contacting physical solid. Further, the CPU  21  calculates the difference dR between the right region starting angle and the angle αR of the right region contacting physical solid. The CPU  21  decides based on a result of the calculation whether or not the angle αL of the left region contacting physical solid and the angle αR of the right region contacting physical solid have varied. 
         [0078]    Then, if the CPU  21  decides that one or both of the angle αL of the left region contacting physical solid and the angle αR of the right region contacting physical solid have changed, then it decides that the angle α of a contacting physical solid has changed. 
         [0079]    Incidentally, also it is estimated that the user may carry out an operation of varying the angle, for example, of the left finger while the housing  11  is not inclined as seen in  FIG. 4E . 
         [0080]    In this instance, since the user varies the angle of the left finger around the root of the finger, different from the case wherein the housing  11  is inclined, the center of gravity of the ball of the fingertip, that is, the region in which the finger contacts the display face of the touch panel  12 , moves. In other words, as seen in  FIG. 4F , the center KpL of gravity of the dark region BkL moves as the angle αL of the left region contacting physical solid varies. 
         [0081]    Accordingly, even if the angle α of the contacting physical solid varies, if the center Kp of gravity of the dark region Bk moves, then it is considered that the housing  11  is not inclined. On the other hand, if the angle α of the contacting physical solid varies and besides the center Kp of gravity of the dark region Bk does not move, then it is considered that the housing  11  is inclined. 
         [0082]    Taking this into consideration, if the CPU  21  decides that the angle α of a contacting physical solid has varied, then it decides whether or not the center Kp of gravity of the dark region Bk has moved from the state wherein the operation mode was changed over to the inclination detection mode. 
         [0083]    In particular, the CPU  21  calculates the distance between the left finger starting gravity center and the center KpL of gravity and the distance between the right finger starting gravity center and the center KpR of gravity and decides based on a result of the calculation that, if the distances are greater than a predetermined threshold value, then the center Kp of gravity has moved. 
         [0084]    It is to be noted that, when the user inclines the housing  11 , the center Kp of gravity may possibly move a little. Accordingly, the threshold value is set to such a degree that movement of the center Kp of gravity when the user inclines the housing  11  and movement of the center Kp of gravity when the housing  11  varies the angle of a finger without inclining the housing  11  can be distinguished from each other. 
         [0085]    If the CPU  21  decides that the angle α of the contacting physical solid has varied and the center Kp of gravity of the dark region Bk has not moved, then it recognizes that the housing  11  is in an inclined state. Meanwhile, if the CPU  21  decides that the angle α of the contacting physical solid has changed and besides the center Kp of gravity of the dark region Bk has moved, then it recognizes that the housing  11  is not in an inclined state. 
         [0086]    Incidentally, when the user inclines the housing  11 , from between the left and right fingers which grip the housing  11 , that finger which exhibits a greater variation in angle reflects the variation of the inclination of the housing  11  accurately. 
         [0087]    Taking this into consideration, the CPU  21  compares the difference dL between the left region starting angle and the angle αL of the left region contacting physical solid and the difference dR between the right region starting angle and the angle αR of the right region contacting physical solid with each other to decide which one of the difference dL and the difference dR is greater. 
         [0088]    Then, the CPU  21  estimates the greater difference as a variation amount of the inclination of the housing  11  from that in the state wherein the inclination of the housing  11  is zero degree, that is, in the state when the mode is changed over to the inclination detection mode, and detects the greater difference as the inclination β of the housing  11 . For example, in the case of  FIG. 4D , since the difference dL is greater than the difference dR, the CPU  21  detects the difference dL as the inclination β of the housing  11 . 
         [0089]    It is to be noted that the CPU  21  detects the counterclockwise direction as a positive direction of the angle α of a contacting physical solid. Therefore, that the angle α of a contacting physical solid varies in the positive direction signifies that the housing  11  is inclined in the negative direction, that is, in the clockwise direction. 
         [0090]    Accordingly, the CPU  21  detects a positive inclination β where the housing  11  is inclined in the clockwise direction, but detects a negative inclination β where the housing  11  is inclined in the counterclockwise direction. For example, where the housing  11  is inclined by 45 degrees in the clockwise direction, the CPU  21  detects that the inclination β is +45 degrees. 
         [0091]    Then, the CPU  21  executes a predetermined process in response to the detected inclination β in various applications. 
         [0092]    In particular, the CPU  21  starts up, for example, an application for reproducing a musical composition and is reproducing a musical composition. At this time, the CPU  21  controls the touch panel  12  to display a title name TN and an artist name AN of the musical composition being reproduced and a sound volume bar MB indicative of the volume of sound being outputted as seen in  FIG. 5A . The sound volume bar MB represents a magnitude of the sound volume with a length of a painted over range. 
         [0093]    Here, it is assumed that, when the CPU  21  is in the inclination detection mode, the user inclines the housing  11 , for example, in the clockwise direction. At this time, the CPU  21  detects a positive inclination β as described hereinabove. Then, the CPU  21  controls the sound outputting section  24  in response to the positive inclination β to raise the volume of sound to be outputted and controls the touch panel  12  to display the sound volume bar MB so that the range within which it is to be covered over is extended from the left toward the right. 
         [0094]    On the other hand, if the inclination β is in the negative, then the CPU  21  controls the sound outputting section  24  to lower the volume of the sound to be outputted and controls the touch panel  12  to display the sound volume bar MB so that the range to be painted over is contracted from the right to the left. It is to be noted that the CPU  21  controls the sound outputting section  24  such that, as the absolute value of the inclination β increases, the adjustment amount of the sound volume increases, but as the absolute value of the inclination β decreases, the adjustment amount of the sound volume decreases. 
         [0095]    Further, the CPU  21  continuously carries out the adjustment of the sound volume in accordance with the inclination β while the user continues to incline the housing  11 . 
         [0096]    Here, it is assumed that the user returns the inclination of the housing  11  to its original state, that is, to the state wherein the changeover to the inclination detection mode was carried out, as seen in  FIG. 5B . At this time, the CPU  21  recognizes that the housing  11  is not inclined, and stops the adjustment of the sound volume. 
         [0097]    Further, it is assumed that, while the application for reproducing a musical component is operating, the CPU  21  controls the touch panel  12  to display, for example, a screen image for selecting an album to be reproduced. In this instance, the CPU  21  controls the touch panel  12  to display jacket photograph images JP, that is, JP 0  to JP 2 , of a plurality of albums in a juxtaposed relationship from the right to the left as seen in  FIG. 6A . At this time, the CPU  21  is in a state wherein it selects an album corresponding to the jacket photograph image JP 1  displayed at the center of the touch panel  12 . 
         [0098]    Here, it is assumed that, when the CPU  21  is in the inclination detection mode, the user inclines the housing  11 , for example, in the clockwise direction. At this time, the CPU  21  detects a positive inclination β as described hereinabove. 
         [0099]    Then, if the CPU  21  recognizes that the detected inclination β is in the positive and the absolute value of the inclination β is higher than the predetermined value, then it causes the jacket photograph images JP displayed on the touch panel  12  to be scrolled from the left to the right as seen in  FIG. 6B  to change over the album to be selected to a next album. At this time, the CPU  21  causes the jacket photograph image JP 2  corresponding to the selected album to be displayed at the center and causes the jacket photograph images JP 3  and JP 1  to be displayed on the left and right of the jacket photograph image JP 2 , respectively. 
         [0100]    On the other hand, if the inclination β is in the negative and the absolute value of the inclination β is higher than the predetermined value, then the CPU  21  controls the touch panel  12  to display the jacket photograph images JP to be displayed on the touch panel  12  so that they are scrolled from the right to the left to change over the album to be selected back to the preceding album. 
         [0101]    Further, while the user continues to incline the housing  11 , the CPU  21  carries out the changeover of the album in accordance with the inclination β continuously. Then, if the user returns the inclination of the housing  11  to its original state as seen in  FIG. 6B , then the CPU  21  recognizes that the housing  11  is not inclined and stops the changeover of an album to be selected. 
         [0102]    Meanwhile, it is assumed that the CPU  21  has started up an application, for example, for reproduction of a dynamic picture and is reproducing a dynamic picture. At this time, the CPU  21  controls the touch panel  12  to display the dynamic picture PV being reproduced as seen in  FIG. 7A . 
         [0103]    Here, it is assumed that, while the CPU  21  is in the inclination detection mode, the user inclines the housing  11 , for example, in the clockwise direction. At this time, the CPU  21  detects a positive inclination β as described hereinabove. Then, the CPU  21  carries out fast forward reproduction of the dynamic picture PV in response to the positive inclination β. 
         [0104]    On the other hand, if the CPU  21  recognizes that the detected inclination β is in the negative, then it causes the dynamic picture PV to be displayed by fast reverse reproduction. It is to be noted that the CPU  21  controls the touch panel  12  to display the dynamic picture PV such that, as the absolute value of the inclination β increases, the speed of fast forward reproduction or fast reverse reproduction increases, but as the absolute value of the inclination β decreases, the speed of fast forward reproduction or fast reverse reproduction of the dynamic picture PV decreases. 
         [0105]    Further, while the user continues to incline the housing  11 , the housing  11  continuously carries out fast forward reproduction or fast reverse reproduction of the dynamic picture PV in accordance with the inclination β. Then, if the user returns the inclination of the housing  11  to its original state as seen in  FIG. 7B , then the CPU  21  recognizes that the housing  11  is not inclined and stops the fast forward reproduction or fast reverse reproduction of the dynamic picture PV being currently reproduced. 
         [0106]    Further, it is assumed that the CPU  21  has started up, for example, an application for accessing an image and images CP, that is, CP 0  and CP 1 , are displayed in a juxtaposed relationship from the right to the left on the touch panel  12  as seen in  FIG. 8A . 
         [0107]    Here, it is assumed that, while the information processing apparatus  10  is in the inclination detection mode, the user inclines the housing  11 , for example, in the clockwise direction. At this time, the CPU  21  detects a positive inclination β as described hereinabove. Then, the CPU  21  controls the touch panel  12  to display the images CP such that they are scrolled from the left to the right in response to the positive inclination β. 
         [0108]    On the other hand, when the inclination β is in the negative, the CPU  21  causes the images CP to be scrolled from the right to the left. It is to be noted that the CPU  21  controls the touch panel  12  such that, as the absolute value of the inclination β increases, the scrolling speed of the images CP increases, but as the absolute value of the inclination β decreases, the scrolling speed of the images CP decreases. 
         [0109]    Further, the CPU  21  carries out scrolling of the images CP in accordance with the inclination β continuously while the user continues to incline the housing  11 . Then, if the user returns the inclination of the housing  11  to its original state as seen in  FIG. 8B , then the CPU  21  recognizes that the housing  11  is not inclined and stops the scrolling of the images CP. 
         [0110]    In this manner, the CPU  21  executes a predetermined process in response to the detected inclination β in various applications. 
       1-3. Inclination Detection Processing Procedure 
       [0111]    Now, an operation processing procedure in the inclination detection process of the information processing apparatus  10  described above, that is, an inclination detection processing procedure RT 1  is described in detail with reference to a flow chart shown in  FIG. 9 . Incidentally, the inclination detection processing procedure RT 1  is executed in accordance with a program installed in the nonvolatile memory  22  by the CPU  21 . 
         [0112]    If an application is started up, then the CPU  21  starts the inclination detection processing procedure RT 1  beginning with step SP 0  and advances its processing to next step SP 1 . 
         [0113]    At step SP 1 , the CPU  21  detects dark regions Bk and intermediate regions Bm on the display face of the touch panel  12  based on the intensity of light received by the optical sensors  12 B. Then, the CPU  21  detects the center Kp of gravity of the dark regions Bk and decides based on the detected centers Kp of gravity whether or not a physical solid contacts each of the opposite left and right regions of the display face. 
         [0114]    If a negative result is obtained at step SP 1 , then this signifies that an operation for changing over the operation mode of the information processing apparatus  10  to the motion detection mode is not carried out by the user. At this time, the CPU  21  advances the processing to step SP 1  thereby to wait that a physical solid is brought into contact each of the left and right regions of the display face of the touch panel  12 . 
         [0115]    On the other hand, if an affirmative result is obtained at step SP 1  because a physical solid contacts each of the opposite left and right regions of the display face of the touch panel  12 , then this signifies that an operation for changing over the operation mode of the information processing apparatus  10  to the inclination detection mode is carried out by the user. At this time, the CPU  21  advances the processing to step SP 2 . 
         [0116]    At step SP 2 , the CPU  21  changes over the operation mode of the information processing apparatus  10  to the inclination detection mode and detects the center Mp of gravity of the intermediate regions Bm. Then, the CPU  21  calculates the angle αL of the left region contacting physical solid and the angle αR of the right region contacting physical solid based on the centers Kp of gravity of the dark regions Bk and the centers Mp of gravity of the intermediate regions Bm and sets the angles αL and αR as a left region starting angle and a right region starting angle, respectively. 
         [0117]    Further, the CPU  21  sets the centers Kp of gravity of the dark regions Bk at this time, that is, the centers of gravity of regions in which the contacting physical solids contact the display face of the touch panel  12 , as the starting centers of gravity. Then, the CPU  21  advances the processing to step SP 3 . 
         [0118]    At step SP 3 , the CPU  21  decides based on the intensity of light received by the optical sensors  12 B whether or not the angle α of each contacting physical solid has changed. 
         [0119]    In particular, the CPU  21  calculates the angle αL of the left region contacting physical solid and the angle αR of the right region contacting physical solid. Then, the CPU  21  calculates the difference dL between the left region starting angle and the angle αL of the left region contacting physical solid and the difference dR between the right region starting angle and the angle αR of the right region contacting physical solid. Then, the CPU  21  decides based on a result of the calculation whether or not the angle α of each contacting physical solid has varied. 
         [0120]    If a negative result is obtained at step SP 3 , then this signifies that the user does not change the angle of the fingers nor inclines the housing  11 . At this time, the CPU  21  returns the processing to step SP 3 , at which it stands by until the angle α of the contacting physical solids varies. 
         [0121]    On the other hand, if an affirmative result is obtained at step SP 3 , then this signifies that the user has varied the angle of the fingers, and at this time, the CPU  21  advances the processing to step SP 4 . 
         [0122]    At step SP 4 , the CPU  21  calculates the distance between the starting gravity center and the center Kp of gravity of the dark region Bk and decides based on a result of the calculation whether or not the center of gravity of the region in which the contacting physical solid is in contact with the display face of the touch panel  12  has moved. 
         [0123]    If an affirmative result is obtained at step SP 4 , then this signifies that the user does not incline the housing  11  although it has varied the angle of the fingers. At this time, the CPU  21  cancels the inclination detection mode and returns the processing to step SP 1 , at which it stands by until a physical solid is brought into contact with each of the left and right regions of the display face of the touch panel  12  again. 
         [0124]    On the other hand, if a negative result is obtained at step SP 4 , then this signifies that the user has inclined the housing  11 , and at this time, the CPU  21  advances the processing to step SP 5 . 
         [0125]    At step SP 5 , the CPU  21  compares the difference dL between the left region starting angle and the angle αL of the left region contacting physical solid and the difference dR between the right region starting angle and the angle αR of the right region contacting physical solid with each other to decide whether or not the difference dL is greater than the difference dR. 
         [0126]    If an affirmative result is obtained at this step SP 5  because the difference dL is equal to or greater than the difference dR, then this signifies that the difference dL accurately reflects the variation of the inclination of the housing  11 . At this time, the CPU  21  advances the processing to step SP 6 . 
         [0127]    At step SP 6 , the CPU  21  detects the difference dL between the left region starting angle and the angle αL of the left region contacting physical solid as the inclination β of the housing  11 . Then, the CPU  21  advances the processing to step SP 8 . 
         [0128]    On the other hand, if a negative result is obtained at step SP 5  because the difference dL is smaller than the difference dR, then this signifies that the different dR accurately reflects the variation of the inclination of the housing  11 . At this time, the CPU  21  advances the processing to step SP 7 . 
         [0129]    At step SP 7 , the CPU  21  detects the difference dR between the right region starting angle and the angle αR of the right region contacting physical solid as the inclination β of the housing  11 , and then the CPU  21  advances the processing to step SP 8 . 
         [0130]    At step SP 8 , the CPU  21  executes a predetermined process in accordance with the inclination β of the housing  11 . Then, the CPU  21  advances the processing to step SP 9 , at which it ends the inclination detection processing procedure RT 1 . 
         [0131]    The CPU  21  detects the inclination β of the housing  11  in accordance with the inclination detection processing procedure RT 1  as described above. 
       1-4. Operation and Effect of the First Embodiment 
       [0132]    In the configuration described above, the information processing apparatus  10  recognizes the shape of a left region contacting physical solid and a right region contacting physical solid, which contact the display face of the touch panel  12  provided on the surface of the housing  11 , based on the intensity of light received by the optical sensors  12 B. 
         [0133]    Then, the information processing apparatus  10  calculates the angle αL of the left region contacting physical solid on the display face of the touch panel  12  based on the shape of the left region contacting physical solid and detects the angle αR of the right region contacting physical solid on the display face of the touch panel  12  based on the shape of the right region contacting physical solid. 
         [0134]    Consequently, the information processing apparatus  10  can detect the angle of the left finger and the angle of the right finger which contact the display face of the touch panel  12  when the user grasps the housing  11 . 
         [0135]    Further, if the information processing apparatus  10  recognizes that a physical solid contacts the left and right regions of the display face of the touch panel  12 , then it recognizes that the user is going to incline the housing  11 . Then, with reference to the angle αL of the left region contacting physical solid and the angle αR of the right region contacting physical solid at this time, the variation of the angle αL of the left region contacting physical solid and the variation of the angle αR of the right region contacting physical solid are calculated. 
         [0136]    Then, the information processing apparatus  10  detects, from between the variation of the angle αL of the left region contacting physical solid and the variation of the angle αR of the right region contacting physical solid, that variation which exhibits a greater variation amount as the inclination β of the housing  11 . 
         [0137]    Consequently, the information processing apparatus  10  can detect the variation of the angle of the fingers griping the housing  11  from the point of time at which the user begins to incline the housing  11 . Since this angle varies in response to inclining of the housing  11 , the inclination β of the housing  11  can be detected accurately based on the variation of the angle. 
         [0138]    Further, the information processing apparatus  10  can detect the variation of the finger, which accurately reflects the variation of the inclination of the housing  11 , as the inclination β of the housing  11  by detecting the angle of the finger which indicates the greater variation as the inclination β of the housing  11 . Consequently, the inclination β of the housing  11  can be detected further accurately. 
         [0139]    Furthermore, the information processing apparatus  10  detects, based on the shape of the contacting physical solid, the center of gravity of a region in which the contacting physical solid contacts the display face of the touch panel  12  and decides whether or not the center of gravity has changed together with the variation of the angle α of the contacting physical solid. 
         [0140]    Then, when the information processing apparatus  10  decides that the center of gravity has not moved together with the variation of the angle α of the contacting physical solid, it recognizes that the housing  11  is inclined, and detects the inclination β of the housing  11  based on the variation of the angle α of the contacting physical solid. 
         [0141]    Consequently, when the user carries out an operation for varying the angle of the finger without inclining the housing  11  such as, for example, a dragging operation, the information processing apparatus  10  is prevented from recognizing in error that the housing  11  is inclined. 
         [0142]    Incidentally, where an inclination detection sensor such as, for example, a gyro sensor is used, even if the user unintentionally inclines the housing  11 , the inclination β of the housing  11  may be detected and a process in accordance with the inclination β may be executed. 
         [0143]    In contrast, when the information processing apparatus  10  recognizes that a physical solid contacts each of the opposite left and right regions of the display face of the touch panel  12 , it changes over the operation mode of the information processing apparatus  10  to the inclination detection mode, in which it detects the inclination β of the housing  11  and executes various processes in response to the inclination β. 
         [0144]    Consequently, the information processing apparatus  10  can execute a process in accordance with the inclination β of the housing  11  when the user touches with the fingers thereof the opposite left and right regions of the display face of the touch panel  12  as an operation for changing over the operation mode of the information processing apparatus  10  to the inclination detection mode. As a result, the information processing apparatus  10  can prevent execution of a process in accordance with the inclination β whose execution is not intended by the user. 
         [0145]    Further, since the information processing apparatus  10  does not execute a process in accordance with the inclination β when the user inclines the housing  11  unintentionally, even a process whose execution is dangerous without an intention of the user such as adjustment of the sound volume can be allocated as a process to be executed in accordance with the inclination β. 
         [0146]    Further, where an inclination detection sensor is used, in order to prevent execution of a process in accordance with the inclination β when the user inclines the housing  11  unintentionally, it is a possible idea to execute a process in accordance with the inclination β when a predetermined button is depressed, when setting is carried out on a menu screen or in a like case. 
         [0147]    However, with the method just described, the process in accordance with the inclination β may not be executed if the user does not carry out a cumbersome operation such as to depress the predetermined button or to carry out setting on the menu screen. 
         [0148]    In contrast, the information processing apparatus  10  can execute a process in accordance with the inclination β of the housing  11  by causing the user to carry out a simple operation of touching with the fingers thereof the opposite left and right regions of the display screen of the touch panel  12 . 
         [0149]    Further, with the information processing apparatus  10 , since the CPU  21  can detect the inclination β of the housing  11  using a result of detection of the touch panel  12 , the inclination β of the housing  11  can be detected with a simpler configuration than that where a gyro sensor is used separately. 
         [0150]    With the configuration described above, the information processing apparatus  10  recognizes the shape of a physical solid contacting the display face of the touch panel  12  and detects the angle α of the contacting physical solid on the display face based on the recognized shape of the contacting physical solid. Then, the information processing apparatus  10  detects the inclination β of the housing  11  based on a variation of the angle α of the contacting physical solid. 
         [0151]    Consequently, the information processing apparatus  10  can detect the angle of a finger contacting the display face of the touch panel  12  when the user grasps the housing  11 . Since the angle of the finger varies in response to inclining movement of the housing  11 , the inclination β of the housing  11  can be detected based on the variation of the angle. Thus, the information processing apparatus  10  can detect the inclination β of the housing  11  without using an inclination detection sensor. 
       1-5. Functional Configuration of the First Embodiment 
       [0152]    Here, a functional configuration of the information processing apparatus  10  principally for the inclination detection process described above is described. Referring to  FIG. 10 , the information processing apparatus  10  functions as a recognition section  31 , an angle detection section  32 , a gravity center detection section  33 , a decision section  34 , an inclination detection section  35  and a control section  36 . 
         [0153]    In the information processing apparatus  10 , the optical sensors  12 B and the CPU  21  described hereinabove function as the recognition section  31 . The recognition section  31  recognizes the shape of a physical solid contacting a predetermined face of the housing  11  of the information processing apparatus  10 , in the present embodiment, with the display face of the touch panel  12  provided on the surface of the housing  11 . 
         [0154]    Further, in the information processing apparatus  10 , the CPU  21  described hereinabove functions as the angle detection section  32 . The angle detection section  32  detects the angle of the physical solid on the predetermined face based on the shape of the physical solid recognized by the recognition section  31 . 
         [0155]    Further, in the information processing apparatus  10 , the CPU  21  described hereinabove functions as the gravity center detection section  33 . The gravity center detection section  33  detects the center of gravity of a portion of the physical solid contacting the predetermined face based on the shape of the physical solid recognized by the recognition section  31 . 
         [0156]    Furthermore, in the information processing apparatus  10 , the CPU  21  described hereinabove functions as the decision section  34 . The decision section  34  decides whether or not the center of gravity detected by the gravity center detection section  33  has moved together with the variation of the angle of the physical solid detected by the angle detection section  32 . 
         [0157]    Further, in the information processing apparatus  10 , the CPU  21  described hereinabove functions as the inclination detection section  35 . The inclination detection section  35  detects, when it is decided by the decision section  34  that the center of gravity has not moved together with the variation of the angle of the physical solid, the inclination of the housing  11  based on the variation of the angle of the physical solid. 
         [0158]    Further, in the information processing apparatus  10 , the CPU  21  described hereinabove functions as the control section  36 . The control section  36  executes a predetermined process in response to the inclination of the housing  11  detected by the inclination detection section  35  when the shape of a plurality of physical solids is recognized by the recognition section  31 . 
         [0159]    With such a functional configuration as described above, the information processing apparatus  10  can functionally implement the inclination detection process described above. 
       2. Second Embodiment 
       [0160]    Now, the second embodiment of is described. The present second embodiment is similar to the first embodiment described hereinabove except that the inclination detection process of the information processing apparatus  10  is different. Therefore, overlapping description of the configuration of the information processing apparatus  10  shown in  FIGS. 2A and 2B  is omitted herein to avoid redundancy. 
       2-1. Inclination Detection Process 
       [0161]    In the following, the inclination detection process in the second embodiment is described in detail. The information processing apparatus  10  executes the inclination detection process when an application is started up. Further, although the information processing apparatus  10  is normally utilized in the horizontally directed state, it can be utilized also in the vertically directed direction. 
         [0162]    If an application, for example, for accessing images is started up, then the CPU  21  controls the touch panel  12  to display an image CP in accordance with a manner in which the housing  11  is utilized in a horizontally directed state, as seen in  FIG. 11A . 
         [0163]    Here, it is assumed that the user grasps the housing  11 , for example, in the horizontally directed state and contacts with a right finger of the user the display face of the touch panel  12 . 
         [0164]    At this time, the CPU  21  carries out the ternary coding process described hereinabove based on the intensity of light received by the optical sensors  12 B and detects a dark region Bk and an intermediate region Bm of the display face of the touch panel  12  as seen in  FIG. 11B . 
         [0165]    When the dark region Bk is detected, the CPU  21  recognizes that a physical solid contacts the display face of the touch panel  12 . 
         [0166]    Then, the CPU  21  detects the center Kp of gravity of the dark region Bk and the center Mp of gravity of the intermediate region Bm and calculates based on the detected centers Kp and Mp of gravity that the angle α of the contacting physical solid is, for example, 120 degrees. Then, the CPU  21  stores the angle α of the contacting physical solid and the center Kp of gravity of the dark region Bk into the nonvolatile memory  22 . 
         [0167]    In this manner, every time the CPU  21  recognizes that a physical solid contacts the display face of the touch panel  12 , it detects the center Kp of gravity of the dark region Bk and the angle α of the contacting physical solid and stores the detected center Kp of gravity and angle α into the nonvolatile memory  22 . 
         [0168]    Then, the CPU  21  reads out the angle α of the contacting physical solid calculated in the preceding operation cycle and the angle α of the contacting physical solid calculated in the current operation cycle from the nonvolatile memory  22  and calculates the difference between them. Then, the CPU  21  decides based on a result of the calculation whether or not the angle α of the contacting physical solid has varied. 
         [0169]    In the case illustrated in  FIGS. 11A and 11B , it is assumed that the user has continued to contact with the right finger the display face of the touch panel  12  without changing the angle of the finger for a period of time after the angle α of the contacting physical solid is calculated in the preceding operation cycle until the angle α of the contacting physical solid is calculated in the present operation cycle. In this instance, since the angle α of the contacting physical solid calculated in the preceding operation cycle and the angle α of the contacting physical solid calculated in the current operation cycle are equal to each other and the difference between them is zero degree, the CPU  21  decides that the angle α of the contacting physical solid has not varied. 
         [0170]    When the CPU  21  decides that the angle α of the contacting physical solid has not varied, it detects the angle α of the contacting physical solid again based on the intensity of light received by the optical sensors  12 B and decides whether or not the angle α of the contacting physical solid has varied. The CPU  21  repeats the process described until the angle α of the contacting physical solid varies. 
         [0171]    Here, it is assumed that the user inclines the housing  11 , for example, by 30 degrees in the clockwise direction around the ball of the fingertip, that is, around the portion of the finger contacting the display face of the touch panel  12  as seen in  FIG. 11C  from the state illustrated in  FIG. 11A . 
         [0172]    At this time, the CPU  21  carries out the ternary coding process described hereinabove based on the intensity of light received by the optical sensors  12 B and detects a dark region Bk and an intermediate region Bm of the display face of the touch panel  12  as seen in  FIG. 11D . Then, the CPU  21  calculates the center Kp of gravity of the dark region Bk and the center Mp of gravity of the intermediate region Bm. 
         [0173]    Then, the CPU  21  calculates based on the center Kp of gravity of the dark region Bk and the center Mp of gravity of the intermediate region Bm that the angle α of the contacting physical solid is, for example, 150 degrees, and stores the angle α of the contacting physical solid and the center Kp of gravity of the dark region Bk into the nonvolatile memory  22 . 
         [0174]    Then, the CPU  21  reads out the angle α of the contacting physical solid calculated in the preceding operation cycle ( FIG. 11B ), which is 120 degrees, and the angle α of the contacting physical solid calculated in the preceding operation cycle, which is 150 degrees, from the nonvolatile memory  22 . Then, the CPU  21  decides that the difference between the angles α of the contacting physical solid is 30 degrees and decides that the angle α of the contacting physical solid has varied. 
         [0175]    When the CPU  21  decides that the angle α of the contacting physical solid has varied, it decides whether or not the center Kp of gravity of the dark region Bk, that is, the center of gravity of the region in which the contacting solid contacts the display face of the touch panel  12 , has moved. In particular, the CPU  21  reads out the distance between the center Kp of gravity detected in the preceding operation cycle and the center Kp of gravity detected in the current operation cycle from the nonvolatile memory  22  and calculates the distance between the two centers Kp of gravity, and then decides based on a result of the calculation whether or not the center Kp of gravity has move. 
         [0176]    In the case shown in  FIG. 11D , since the user has inclined the housing  11  around the center of gravity of the region of the display face of the touch panel  12  in which the finger contacts, the center of gravity of the region of the display face of the touch panel  12  in which the finger contacts has not moved from the state in the preceding operation cycle illustrated in  FIG. 11B . Accordingly, the CPU  21  decides that the center Kp of gravity of the dark region Bk has not moved. 
         [0177]    When the CPU  21  decides that the angle α of the contacting physical solid has varied and besides the center Kp of gravity of the dark region Bk has not moved, it recognizes that the housing  11  is not inclined. 
         [0178]    On the other hand, if the CPU  21  decides that the angle α of the contacting physical solid has changed and besides the center Kp of gravity has moved, then it recognizes that the user has carried out an operation for varying the angle of the finger while the housing  11  is not inclined. 
         [0179]    If the CPU  21  recognizes that the housing  11  has been inclined, then it decides whether or not the movement of the contacting physical solid stopped when the angle α of the contacting physical solid was calculated in the preceding operation cycle. In particular, the CPU  21  reads out the angle α of the contacting physical solid calculated in the preceding operation cycle and the angle α of the contacting physical solid calculated in the second preceding operation cycle from the nonvolatile memory  22 . Then, the CPU  21  calculates the difference between the angles α and decides based on a result of the calculation whether or not the movement of the contacting physical solid stopped when the angle α of the contacting physical solid was calculated in the preceding cycle. 
         [0180]    In the case illustrated in  FIG. 11D , since the difference between the angle α of the contacting physical solid in the preceding operation cycle illustrated in  FIG. 11B  and the angle α of the contacting physical solid calculated in the second preceding operation cycle is zero degree, the CPU  21  decides that the movement of the contacting physical solid stopped when the angle α of the contacting physical solid in the preceding operation cycle was calculated. 
         [0181]    When the CPU  21  decides that the movement of the contacting physical solid stopped when the angle α of the contacting physical solid was calculated in the preceding operation cycle, the CPU  21  recognizes that the time in this instance is a point of time at which the user began to vary the angle of the finger, that is, the user began to incline the housing  11 . Then, the CPU  21  sets the angle α of the contacting physical solid calculated in the preceding operation cycle, that is, 120 degrees, as the starting angle. 
         [0182]    Then, the CPU  21  calculates the difference d between the starting angle and the angle α of the contacting physical solid calculated in the current operation cycle and detects the difference d as the inclination β of the housing  11 . In the case illustrated in  FIG. 11D , since the starting angle is 120 degrees and the angle α of the finger calculated in the current operation cycle is 150 degrees, the CPU  21  calculates that the difference d is 30 degrees and thus detects the inclination β of the housing  11  as 30 degrees. 
         [0183]    Then, the CPU  21  decides whether or not the absolute value of the inclination β of the housing  11  is greater than 90 degrees. In the case illustrated in FIG.  11 D, since the inclination β of the housing  11  is 30 degrees, the CPU  21  decides that the absolute value of the inclination β of the housing  11  is not greater than 90 degrees. 
         [0184]    When the CPU  21  decides that the absolute value of the inclination β of the housing  11  is not greater than 90 degrees, it does not carry out a process in accordance with the inclination β of the housing  11 , but carries out the process described hereinabove again to detect the inclination β of the housing  11 . 
         [0185]    Here, it is assumed that, for example, the user further inclines the housing  11  around the region of the display screen of the touch panel  12  in which the finger contacts from the state illustrated in  FIG. 11C  until the housing  11  is placed into a vertically directed state as seen in  FIG. 11E . 
         [0186]    At this time, the CPU  21  carries out the ternary coding process described hereinabove based on the intensity of light received by the optical sensors  12 B and detects a dark region Bk and an intermediate region Bm of the display screen of the touch panel  12  as seen in  FIG. 11F . Then, the CPU  21  calculates that the angle α of the contacting physical solid is, for example, 210 degrees as described hereinabove and stores the angle α of the contacting physical solid and the center Kp of gravity of the dark region Bk into the nonvolatile memory  22 . 
         [0187]    Then, the CPU  21  calculates that the difference between the angle α of the contacting physical solid calculated in the preceding operation cycle illustrated in  FIG. 11D , which is 150 degrees, and the angle α of the contacting physical solid calculated in the current operation cycle, which is 210 degrees, is 60 degrees. The CPU  21  thus decides that the angle α of the contacting physical solid has varied. 
         [0188]    Then, when the CPU  21  decides that the angle α of the contacting physical solid has varied, it decides whether or not the center Kp of gravity has moved. In the case illustrated in  FIG. 11F , the CPU  21  decides based on the center Kp of gravity calculated in the preceding operation cycle and the center Kp of gravity calculated in the current operation cycle that the center Kp of gravity has not moved. 
         [0189]    Then, when the CPU  21  decides that the center Kp of gravity has not moved, it decides whether or not the movement of the contacting physical solid stopped when it calculated the angle α of the contacting physical solid in the preceding operation cycle. In the case illustrated in  FIG. 11F , the CPU  21  calculates that the difference between the angle α of the contacting physical solid calculated in the preceding operation cycle, which is 150 degrees, and the angle α of the contacting physical solid calculated in the second preceding operation cycle, which is 120 degrees, is 30 degrees. Thus, the CPU  21  decides that, when it calculated the angle α of the contacting physical solid in the preceding operation cycle, the contacting physical solid was moving. 
         [0190]    When the CPU  21  decides that, when it calculated the angle α of the contacting physical solid in the preceding operation cycle, the contacting physical solid was moving, it recognizes that the user is currently inclining the housing  11  and a starting angle has already been set. Then, the CPU  21  calculates that the starting angle, which is 120 degrees, and the angle α of the contacting physical solid calculated in the present operation cycle, which is 210 degrees, is 90 degrees. Thus, the CPU  21  detects that the inclination β of the housing  11  is 90 degrees. 
         [0191]    Then, when the CPU  21  decides that the absolute value of the inclination β of the housing  11  is higher than 90 degrees, it recognizes that the housing  11  is grasped in a vertically directed state by the user and rotates the image CP by 90 degrees in accordance with the inclination β of the housing  11 . 
         [0192]    In particular, when the inclination β is 90 degrees, since the housing  11  is inclined in the clockwise direction, the CPU  21  rotates the image CP by 90 degrees in the counterclockwise direction as seen in  FIG. 11E . On the other hand, if the inclination β is −90 degrees, then since the housing  11  is inclined in the counterclockwise direction, the CPU  21  rotates the image CP by 90 degrees in the clockwise direction. 
         [0193]    Consequently, even if the user inclines the housing  11  until it is placed into a vertically directed state, the CPU  21  can cause the image CP to be displayed in accordance with the horizontally directed state, and consequently, the user can access the image CP readily. 
         [0194]    It is to be noted that, when the image CP is rotated, the CPU  21  controls the touch panel  12  to display the image CP in a reduced scale so that the image CP may fit in the display screen of the touch panel  12 . 
         [0195]    In the manner, the CPU  21  can detect the inclination β and execute a predetermined process in accordance with the inclination β. 
       2-2. Inclination Detection Processing Procedure 
       [0196]    Now, an operation processing procedure (hereinafter referred to also as inclination detection processing procedure) RT 2  in the inclination detection process by the information processing apparatus  10  is described in detail with reference to a flow chart shown in  FIG. 12 . It is to be noted that the inclination detection processing procedure RT 2  is executed by the CPU  21  in accordance with a program installed in the nonvolatile memory  22 . 
         [0197]    If an application is started up, then the CPU  21  starts the inclination detection processing procedure RT 2  beginning with step SP 100  and advances its processing to next step SP 101 . 
         [0198]    At step SP 101 , the CPU  21  detects a dark region Bk and an intermediate region Bm on the display face of the touch panel  12  based on the intensity of light received by the optical sensors  12 B. Then, the CPU  21  decides whether or not a physical solid contacts the display face of the touch panel  12  based on a result of the detection. 
         [0199]    If a negative result is obtained at step SP 101 , then this signifies that a finger of the user is not in contact with the display face of the touch panel  12 . At this time, the CPU  21  returns the processing to step SP 101  to stand by until a physical solid contacts the display face of the touch panel  12 . 
         [0200]    On the other hand, if an affirmative result is obtained at step SP 101 , then this signifies that a finger of the user is in contact with the display face of the touch panel  12 , and the CPU  21  advances the processing to step SP 102 . 
         [0201]    At step SP 102 , the CPU  21  detects the center Kp of gravity of the dark region Bk and the center Mp of gravity of the intermediate region Bm. Then, the CPU  21  calculates the angle α of the contacting physical solid based on the center Kp of gravity of the dark region Bk and the center Mp of gravity of the intermediate region Bm and advances the processing to step SP 103 . 
         [0202]    At step SP 103 , the CPU  21  calculates the difference between the angle α of the contacting physical solid calculated in the preceding operation cycle and the angle α of the contacting physical solid calculated in the current operation cycle and decides based on a result of the calculation whether or not the angle α of the contacting physical solid has varied. 
         [0203]    If a negative result is obtained at step SP 103 , then this signifies that the user has not varied the angle of the finger and has not inclined the housing  11 . At this time, the CPU  21  returns the processing to step SP 101  to stand by again until a physical solid contacts the display face of the touch panel  12 . 
         [0204]    On the other hand, if an affirmative result is obtained at step SP 103 , then this signifies that the user has varied the angle of the finger. At this time, the CPU  21  advances the processing to step SP 104 . 
         [0205]    At step SP 104 , the CPU  21  calculates the distance between the center Kp of gravity of the dark region Bk detected in the preceding operation cycle and the center Kp of gravity of the dark region Bk detected in the current operation cycle and decides whether or not the center of gravity of the region in which the contacting physical solid contacts with the display face of the touch panel  12  has moved based on a result of the calculation. 
         [0206]    If a negative result is obtained at step SP 104 , then this signifies that, while the user has varied the angle of the finger, the housing  11  has not been inclined. At this time, the CPU  21  returns the processing to step SP 101  to stand by again until a physical solid contacts the display face of the touch panel  12 . 
         [0207]    On the other hand, if an affirmative result is obtained at step SP 104 , then this signifies that the user has inclined the housing  11 . At this time, the CPU  21  advances the processing to step SP 105 . 
         [0208]    At step SP 105 , the CPU  21  calculates the difference between the angle α of the contacting physical solid calculated in the second preceding operation cycle and the angle α of the contacting physical solid calculated in the preceding operation cycle and decides based on a result of the calculation whether or not movement of the contacting physical solid stopped when the angle α of the contacting physical solid was calculated in the preceding operation cycle. 
         [0209]    If an affirmative result is obtained at step SP 105 , then this signifies that the timing at which the angle α of the contacting physical solid was calculated in the preceding operation cycle was a point of time at which the user started to incline the housing  11 . At this time, the CPU  21  advances the processing to step SP 106 . 
         [0210]    At step SP 106 , the CPU  21  sets the angle α of the contacting physical solid in the preceding operation cycle as a starting angle and advances the processing to step SP 107 . 
         [0211]    On the other hand, if a negative result is obtained at step SP 105 , then this signifies that the user inclined the housing  11  already when the angle α of the contacting physical solid was calculated in the preceding operation cycle and the starting angle is set already. At this time, the CPU  21  advances the processing to step SP 107 . 
         [0212]    At step SP 107 , the CPU  21  calculates the difference d between the starting angle and the angle α of the contacting physical solid in the current operation cycle and detects the difference d as the inclination β of the housing  11  and then advances the processing to step SP 108 . 
         [0213]    At step SP 108 , the CPU  21  decides whether or not the absolute value of the inclination β of the housing  11  is greater than 90 degrees. 
         [0214]    If a negative result is obtained at step SP 108 , then this signifies that the housing  11  is grasped in a horizontally directed state by the user. At this time, the CPU  21  returns the processing to step SP 101  to stand by again until a physical solid contacts the display face of the touch panel  12 . 
         [0215]    On the other hand, if an affirmative result is obtained at step SP 108 , then this signifies that the housing  11  is grasped in a vertically directed state by the user. At this time, the CPU  21  advances the processing to step SP 109 . 
         [0216]    At step SP 109 , the CPU  21  rotates an image CP displayed on the touch panel  12  in a clockwise direction or a counterclockwise direction by 90 degrees in accordance with the inclination β and advances the processing to step SP 110 , at which it ends the inclination detection processing procedure RT 2 . 
         [0217]    The CPU  21  detects the inclination of the housing  11  in accordance with such an inclination detection processing procedure RT 2  as described above. 
       2-3. Operation and Effect of the Second Embodiment 
       [0218]    In the configuration described above, the information processing apparatus  10  detects an angle α of a contacting physical solid on the display face based on the shape of the contacting physical solid every time the shape of the physical solid contacting with the display face of the touch panel  12  is recognized. 
         [0219]    Then, the information processing apparatus  10  compares the angle α of the contacting physical solid detected in the preceding operation cycle and the angle α of the contacting physical solid detected in the current operation cycle. Then, if it is decided that the angle α of the contacting physical solid has varied, then the information processing apparatus  10  decides whether or not movement of the contacting physical solid stopped when the angle α of the contacting physical solid was detected. 
         [0220]    Then, if it is decided that the movement of the contacting physical solid stopped when the angle α of the contacting physical solid was detected in the preceding operation cycle, then it is recognized by the information processing apparatus  10  that the point of time described is a point of time at which the user started to incline the housing  11 , and the variation of the angle α of the contacting physical solid is detected with reference to the angle α of the contacting physical solid at the point of time. 
         [0221]    Consequently, the information processing apparatus  10  can detect the variation of the angle of the finger grasping the housing  11  from the point of time at which the user started to incline the housing  11 . 
         [0222]    As a result, the information processing apparatus  10  can detect the inclination β of the housing  11  accurately based on the variation of the angle of the finger grasping the housing  11  which varies in response to inclination of the housing  11  also where the user grasps the housing  11  by one hand. 
         [0223]    Further, the information processing apparatus  10  detects the center of gravity of the region in which the contacting physical solid contacts the display face of the touch panel  12  based on the shape of the contacting physical solid and decides whether or not the center of gravity has moved together with the variation of the angle α of the contacting physical solid. 
         [0224]    Then, when the information processing apparatus  10  decides that the center of gravity has not moved together with the variation of the angle α of the contacting physical solid, it recognizes that the housing  11  is inclined, and detects the inclination β based on the variation of the angle α of the contacting physical solid. 
         [0225]    Consequently, also where the user grasps the housing  11  by one hand, when the user carries out an operation of varying the angle of its finger without inclining the housing  11 , the information processing apparatus  10  can be prevented from recognizing in error that the housing  11  is inclined. 
         [0226]    It is to be noted that the functional configuration of the information processing apparatus  10  in the second embodiment is similar to that of the information processing apparatus of the first embodiment described hereinabove with reference to  FIG. 10  except that it does not include the control section  36 . In other words, the information processing apparatus  10  in the second embodiment functions as the recognition section  31 , the angle detection section  32 , the gravity center detection section  33 , the decision section  34  and the inclination detection section  35 . 
       3. Additional Embodiments 
     3-1. Additional Embodiment 1 
       [0227]    It is to be noted that, in the first embodiment described hereinabove, the CPU  21  detects the variation of the angle αL of the left region contacting physical solid and the variation of the angle αR of the right region contacting physical solid and detects a greater one of the variations as the inclination β of the housing  11 . 
         [0228]    However, the CPU  21  may detect the variation of the angle αL of the left region contacting physical solid and the variation of the angle αR of the right region contacting physical solid and use various other methods to detect the inclination β of the housing  11  based on the detected variations. 
         [0229]    For example, the CPU  21  may calculate an average value of the variation of the angle αL of the left region contacting physical solid and the variation of the angle αR of the right region contacting physical solid and detect the average value as the inclination β of the housing  11 . 
         [0230]    Or, for example, the CPU  21  may detect the variation in angle of that one of the left region contacting physical solid and the right region contacting physical solid with regard to which the distance of movement of the center of gravity of the region in which a finger contacts the display face of the touch panel  12  is shorter as the inclination β of the housing  11 . 
         [0231]    This is because that finger with regard to which the distance of movement of the center of gravity of the region in which the finger contacts the display face of the touch panel  12  is shorter provides the center of rotation when the housing  11  is inclined and the variation of the corresponding angle reflects the variation of the inclination of the housing  11  comparatively accurately. 
         [0232]    Alternatively, the CPU  21  may detect the variation in angle of, for example, that one of the left region contacting physical solid and the right region contacting physical solid with regard to which the area of the region in which the finger contacts the display face of the touch panel  12  is smaller as the inclination β of the housing  11 . 
         [0233]    This is because the finger which contacts over a greater area grasps the housing  11  comparatively strongly and, even if the housing  11  is inclined, the variation in angle is smaller and therefore the variation of the inclination of the housing  11  is less liable to be reflected. 
         [0234]    However, the CPU  21  may alternatively recognize three or more contacting solids, detect the angle α of each contacting physical solid and detect that angle α of the contacting physical solid which exhibits the greatest variation as the inclination β of the housing  11 . 
       3-2. Additional Embodiment 2 
       [0235]    Further, in the first embodiment described hereinabove, if the CPU  21  decides that a physical solid contacts each of the opposite left and right regions of the display face of the touch panel  12 , then it changes the operation mode of the information processing apparatus  10  into the inclination detection mode, in which it detects the inclination β of the housing  11 . 
         [0236]    However, when the CPU  21  detects that a plurality of physical solids contact the display face of the touch panel  12  irrespective of whether the touched locations are the opposite left and right regions of the display face, the CPU  21  may change over the operation mode of the information processing apparatus  10  to the inclination detection mode, in which it detects the inclination β of the housing  11 . 
         [0237]    Or, when the CPU  21  decides that a predetermined operation is carried out for the display face of the touch panel  12 , for example, an operation of moving a contacting physical solid in such a manner as to draw a circle is carried out, it may change over the operation mode of the information processing apparatus  10  to the inclination detection mode, in which it detects the inclination β of the housing  11 . 
       3-3. Additional Embodiment 3 
       [0238]    Further, in the first and second embodiments described hereinabove, the CPU  21  executes various processes such as adjustment of the sound volume, changeover of a selected album, fast forward and reverse reproduction of dynamic pictures, scrolling of images and rotation of an image in accordance with the inclination β. 
         [0239]    However, the CPU  21  may additionally execute various other processes such as chapter forward selection and chapter reverse selection of dynamic pictures, a game which utilizes the inclination and so forth in accordance with the inclination β. 
         [0240]    In the first embodiment described hereinabove, the CPU  21  adjusts the degree by which various processes are to be carried out, for example, by changing the amount of adjustment of the sound volume in response to the absolute value of the inclination β. 
         [0241]    However, the CPU  21  may execute various processes depending upon whether the inclination β is in the positive or negative irrespective of the absolute value of the inclination β such as to raise the sound volume by a predetermined amount when the inclination β is in the positive but lower the sound volume by a predetermined amount when the inclination β is in the negative. 
       3-4. Additional Embodiment 4 
       [0242]    Further, in the first and second embodiments described hereinabove, the CPU  21  detects the inclination β of the housing  11  where the center of gravity of the region in which a contacting physical solid contacts the display face of the touch panel  12  even if the angle α of the contacting physical solid varies. 
         [0243]    However, the CPU  21  may detect the inclination β of the housing  11  otherwise if the angle α of the contacting physical solid varies irrespective of whether or not the center of gravity of the region in which the contacting physical solid contacts the display face of the touch panel  12 . 
       3-5. Additional Embodiment 5 
       [0244]    Further, in the first and second embodiments described hereinabove, the CPU  21  detects the angle α of a contacting physical solid based on the center of gravity of a region in which the contacting physical solid contacts the display face of the touch panel  12  and the center of gravity in another region in which the contacting physical solid is positioned in the proximity of the display face. 
         [0245]    However, the CPU  21  may detect the angle α of the contacting physical solid alternatively by various other methods. For example, the CPU  21  may recognize the shape of a region in which the contacting physical solid contacts the display face of the touch panel  12 , detect a rectangle which surrounds the shape of the region and has the smallest area, and detect the angle α of the contacting physical solid from the angle of the rectangle on the display face. 
       3-6. Additional Embodiment 6 
       [0246]    Further, in the first and second embodiments described hereinabove, the touch panel  12  of the optical sensor type is used. However, a touch panel of any other type such as, for example, a touch panel of the capacitance type may be used only if it can recognize the shape of a physical solid which contacts the display face of the touch panel  12 . 
       3-7. Additional Embodiment 7 
       [0247]    Further, in the first and second embodiments described hereinabove, the touch panel  12  provided on the surface of the housing  11  is used. However, a touch panel provided on the rear face of the housing  11  may be used alternatively. 
         [0248]    In this instance, the CPU  21  detects the inclination of the housing  11  in response to a variation of the angle of a physical solid which contacts the touch panel provided on the rear face of the housing  11 . Consequently, since also the angle of a finger contacting the rear face of the housing  11  varies in response to inclination of the housing  11 , the inclination β of the housing  11  can be detected based on this angle. 
         [0249]    Alternatively, for example, a touch panel for exclusive use for ordinary touching operation having a display section may be provided on the surface of the housing  11  while another touch panel for inclination detection which does not have a display section is provided on the rear face of the housing  11 . 
         [0250]    Consequently, when the user varies the angle of a finger without inclining the housing  11 , the CPU  21  can be prevented from recognizing in error that the housing  11  is inclined. This is because, when the user varies the angle of a finger without inclining the housing  11 , although the user varies the angle of the finger contacting the surface of the housing  11 , which is the face for which an ordinary touching operation is to be carried out, it is estimated that the user does not vary the angle of the finger contacting the rear face of the housing  11 . 
       3-8. Additional Embodiment 8 
       [0251]    Further, in the first and second embodiments described hereinabove, the program for executing the inclination detection process is stored in the nonvolatile memory  22 . 
         [0252]    However, the program just above may otherwise be recorded on a predetermined recording medium such as, for example, a CD (Compact Disc) such that the CPU  21  reads out the program from the recording medium and executes the same. Alternatively, the CPU  21  may download the program from a predetermined server on the Internet and install the program into the nonvolatile memory  22 . 
       3-9. Additional Embodiment 9 
       [0253]    Further, in the first and second embodiments, the information processing apparatus  10  as an information processing apparatus includes the optical sensors  12 B as the recognition section  31 , recognition section  31 , angle detection section  32 , gravity center detection section  33 , decision section  34 , inclination detection section  35  and CPU  21  as the control section  36 . 
         [0254]    However, the functioning sections described above may be configured from various types of hardware or software if similar functions are achieved. For example, each of the recognition section  31 , angle detection section  32 , gravity center detection section  33 , decision section  34 , inclination detection section  35  and control section  36  may be implemented from a separate piece of hardware. 
         [0255]    Further, the present invention may be applied to various outer information processing apparatus such as a portable audio player, a PDA (Personal Digital Assistant) and a portable telephone set only if they have a similar configuration. 
       3-10. Additional Embodiment 10 
       [0256]    Further, the present invention is not limited to the first and second embodiments described hereinabove nor to the additional embodiments 1 to 9. In other words, the present invention is applied to those forms which include arbitrary combinations of some or all of the first and second embodiments described hereinabove and the additional embodiments 1 to 9 described above or those forms which include arbitrary elements extracted from the embodiments mentioned. 
         [0257]    For example, the first embodiment and the second embodiment described hereinabove may be combined. In this instance, when the CPU  21  recognizes that one physical solid contacts the touch panel  12 , it may detect the inclination β of the housing  11  by the inclination detection process according to the second embodiment, but when the CPU  21  recognizes that two physical solids contact the touch panel  12 , it may detect the inclination β of the housing  11  by the inclination detection process according to the first embodiment. 
         [0258]    The information processing apparatus, inclination detection method and inclination detection program of the present invention can be applied to various information processes such as, for example, a portable audio player, a PDA and a portable telephone set. 
         [0259]    The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2009-100171 filed in the Japan Patent Office on Apr. 16, 2009, the entire content of which is hereby incorporated by reference. 
         [0260]    While embodiments have been described using specific terms, such description is for illustrative purpose only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.