Patent Publication Number: US-9418285-B2

Title: Information processing apparatus and input control method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of International Application PCT/JP2011/064457 filed on Jun. 23, 2011 and designated the U.S., the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The disclosures herein generally relate to an information processing apparatus, an input control method and an input control program that control key inputs without using a physical keyboard. 
     BACKGROUND 
     In recent years, keyboardless devices have become widely used that include smart phones and tablet-type devices such as a slate PC (Personal Computer) and an iPad (trademark). However, such keyboardless devices are not implemented with a character input interface that has a competitive operational feeling like a QWERTY-type physical keyboard, which is one of the most significant disadvantages for a user who needs to input a long passage. 
     For portable terminals such as a smart phone and the like, an input interface using a numeric keypad is most widely used that may be implemented with a touch panel or a physical keypad. If the number of types of characters is greater than the number of keys displayed on a screen, a key is assigned with multiple character types where a character is selected by pushing down the key one or more times. For example, a ten-key numeric keypad is displayed on a screen in which a key labeled with “2” has “A”, “B” and “C” assigned, with which one of the characters is selected by pushing down the key for a predetermined number of times. 
     Also, iPhone (trademark) is provided with an interface called “flick input”. With flick input, if a predetermined key is pushed down, characters assigned to the key are displayed on the left, right, top and bottom of the key. 
     For example, a ten-key numeric keypad is displayed on a screen in which a key labeled with “2” has “A”, “B” and “C” assigned, and if “A” is pushed down, “B” and “C” are displayed on the left and top of “A”, respectively. By lifting up the pushing finger at the position of one of the keys, the character type at the position is selected. Flick input can make the number of key pushes fewer than the method of selecting a character by multiple pushes. 
     The input methods described above allow input with one hand, which may be suitable for input operations during travel such as a train ride or for input of a short sentence. However, as portable terminals become smaller and so do character input areas on the terminals, operability of the keys become worse, especially when inputting a long sentence. 
     As for tablet-type devices, comparatively larger touch panel displays, such as a 10-inch type, are usually adopted, on which a software keyboard, for example, a QWERTY-type full keyboard, is displayed. 
     If such a software keyboard is displayed on a tablet-type device with a practical size, the keyboard may occupy a large display area on the screen, which makes it difficult to view an application display. 
     Regarding this matter, there is a technology for key inputs that detects positions of fingertips on a virtual keyboard. For example, fingertips of an operator are captured using two cameras, and three dimensional positions of the fingertips are detected from the captured images, with which keys on the virtual keyboard corresponding to the positions are determined (Patent Documents 1 and 2). 
     RELATED-ART DOCUMENTS 
     Patent Documents 
     
         
         [Patent Document 1] Japanese Laid-open Patent Publication No 2001-282428 
         [Patent Document 2] Japanese Laid-open Patent Publication No 2003-288156 
       
    
     With such a conventional technology, although a physical keyboard is not required, two cameras are required instead. In the first place, a terminal without a physical keyboard (also called a “physical keyboardless terminal”) is targeted for a thin, small device by not installing a physical keyboard. 
     However, the conventional technology needs two cameras installed for detecting three dimensional movement, with which images of fingers of an operator need to be captured from the front and from above that restricts mount positions of the two cameras. Therefore, a device installed with two cameras at limited mount positions does not have an advantage in terms of portability and cost. 
     SUMMARY 
     According to at least one embodiment of the present invention, an information processing apparatus includes an image capturing section to capture an image of a hand; an extracting section to extract a hand area from the captured image; a reference line determining section to determine a reference pushdown line in the image on the hand area; a determining section to determine a pushdown move if the bottom part of the hand area comes below the reference pushdown line; a first position determining section to determine a depth position based on an aspect ratio of the hand area if the pushdown move is determined; a second position determining section to determine a lateral position based on a position of the bottom part of the hand area if the pushdown move is determined; and an input key determining section to determine an input key from the determined depth position and lateral position. 
     The object and advantages of the embodiment will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view illustrating an example of a use case of an information processing apparatus according to an embodiment; 
         FIG. 2  is a schematic view illustrating an example of hardware of an information processing apparatus; 
         FIG. 3  is a block diagram illustrating an example of functions of an information processing apparatus; 
         FIG. 4  is a schematic view illustrating an example of extracted hand areas; 
         FIG. 5  is a schematic view illustrating an example of a virtual keyboard; 
         FIG. 6  is a schematic view illustrating an example of a reference pushdown line; 
         FIG. 7  is a schematic view illustrating an example of a key pushdown move; 
         FIG. 8  is a schematic view illustrating an example of hand areas evenly partitioned; 
         FIG. 9  is a schematic view illustrating an example of threshold values; 
         FIG. 10A  is a schematic view illustrating an example of a hand area when operating an upper row; 
         FIG. 10B  is a schematic view illustrating an example of a hand area when operating a middle row; 
         FIG. 10C  is a schematic view illustrating an example of a hand area when operating a lower row; 
         FIG. 11  is a schematic view illustrating an example of input key determination; 
         FIG. 12  is a flowchart illustrating an example of a calibration procedure according to a first embodiment; 
         FIG. 13  is a flowchart illustrating an example of a key input procedure according to the first embodiment; 
         FIG. 14  is a flowchart illustrating an example of a hand area extracting procedure; and 
         FIG. 15  is a flowchart illustrating an example of a key input procedure according to a third embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First, a use case of an information processing apparatus will be described according to embodiments.  FIG. 1  is a schematic view illustrating an example of a use case of the information processing apparatus  10  according to the embodiments. In the example illustrated in  FIG. 1 , for example, a camera  104  of the information processing apparatus  10  is positioned in a lower part, and the information processing apparatus  10  is set in an upright state with respect to a plane. At this moment, a user puts both hands within a range that can be captured by the camera  104 , and simulates operations on a keyboard. In this case, it is desirable that the user can do touch typing. 
     The camera  104  captures images of movements of both hands of the user. The information processing apparatus  10  estimates and detects three dimensional positions of fingertips of the hands from the captured images taken by the camera  104 . The information processing apparatus  10  determines keys depending on the detected three dimensional positions to receive key inputs. 
     The information processing apparatus  10  is a physical keyboardless terminal, for example, a smart phone, a slate PC, a tablet-type device, or the like. In the following, the embodiments of the present invention will be described with reference to the drawings. According to at least one embodiment of the present invention, it is possible to determine an input command depending on a three dimensional position of a finger where the position is estimated based on a captured image taken by a camera in a single direction. 
     [First Embodiment] 
     &lt;Hardware&gt; 
       FIG. 2  is a schematic view illustrating an example of hardware of the information processing apparatus  10 . The information processing apparatus  10  illustrated in  FIG. 1  includes a control section  101 , a main memory section  102 , an auxiliary storage section  103 , a camera  104 , and a display section  105 . These sections are connected with each other via a bus for data transmission and reception. 
     The control section  101  is a CPU (Central Processing Unit) that controls devices and operates on data. Also, the control section  101  is an execution unit that executes a program stored in the main memory section  102  or the auxiliary storage section  103 . Also, the control section  101  operates and processes input data to output it to the display section  105 , the auxiliary storage section  103 , or the like. 
     The main memory section  102  is a ROM (Read-Only Memory), a RAM (Random Access Memory) and the like, which is a storage device to store or to temporarily store an OS, or the basic software, programs such as application software or the like, and data. 
     The auxiliary storage section  103  is an HDD (Hard Disk Drive) or the like, which is a storage device to store data related to the application software and the like. 
     The camera  104  includes, for example, a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor to capture, for example, hands of a user. 
     The display section  105  is configured with an LCD (Liquid Crystal Display) or the like, to display data input from the control section  101 . 
     Here, although the embodiments are described with the example in which the information processing apparatus  10  has the camera  104  built in, the camera  104  is not necessarily a mandatory element of the information processing apparatus  10 . The information processing apparatus  10  may be connected with an external camera to capture an image from the camera by the control section  101 . 
     Also, the information processing apparatus  10  may further include a drive device as an interface to a recording medium, a network interface section to communicate with other devices, and the like. 
     For example, the drive device reads a program from a recording medium (for example, a flexible disk) to install it into the auxiliary storage section  103 . 
     Also, a recording medium stores a predetermined program, which is installed into the information processing apparatus  10  via the drive device. The installed predetermined program can be executed by the information processing apparatus  10 . 
     The network interface section is an interface between a peripheral device, which has a communication function connected with a network such as a LAN (Local Area Network) or a WAN (Wide Area Network) configured with wired and/or wireless network data transmission lines, and the information processing apparatus  10 . 
     &lt;Functions&gt; 
       FIG. 3  is a block diagram illustrating an example of functions of the information processing apparatus  10 . In the example illustrated in  FIG. 3 , the information processing apparatus  10  includes a key input section  201 , an image capturing section  202 , and a storage section  203 . 
     The key input section  201  may be implemented by, for example, the control section  101  and the main memory section  102  as a working memory, the image capturing section  202  may be implemented by, for example, the camera  104 , and the storage section  203  may be implemented by, for example, the main memory section  102  or the auxiliary storage section  103 . 
     The image capturing section  202  captures an image having a range, for example, including hands of a user. The key input section  201  obtains the captured image from the image capturing section  202 , detects three dimensional positions of fingers in the captured image, and determines an input command based on the three dimensional positions of the fingers. The input command is, for example, a character code. The input command is stored into the storage section  203 . 
     The storage section  203  stores data obtained from the key input section  201 , for example, an input command. 
     Next, the key input section  201  will be described in detail. The key input section  201  includes an extracting section  211 , a reference line determining section  212 , a determining section  213 , a lateral position determining section  214 , a depth position determining section  215 , and an input key determining section  216 . 
     Here, functions of the sections will be described that are relevant to a calibration procedure and a key input procedure, which are parts of an input control procedure executed by the information processing apparatus  10  according to the first embodiment. 
     (Calibration Procedure) 
     The calibration procedure is executed when a user places both hands at home positions in front of the camera  104  while the input control procedure is being executed. For example, a user may place both hands on a desk. 
     The extracting section  211  extracts an area of hands (also called a “hand area”) from the captured image input from the image capturing section  202 . Extraction of a hand area from the captured image may be done with a method based on extracting a flesh color of hands, a method based on characteristic values of the form of hands registered in advance, and the like. 
     Also, the extracting section  211  may delete a palm area from a hand area as will be described later. To delete a palm area, for example, edges of fingers may be extracted. Although it is assumed that a palm area is deleted from a hand area in the following example, a palm area does not necessarily need to be deleted. A hand area may be extracted by one of the publicly known technologies. 
     The extracting section  211  calculates an aspect ratios R of left and right hand areas. Aspect ratios R are obtained with formula (1), (2). For example, the extracting section  211  may obtain a circumscribed rectangle of a hand area and calculate the aspect ratio of the circumscribed rectangle for calculating the aspect ratio of the hand area.
 
RR=H (Right)/W(Right)  formula (1)
 
RL=H (Left)/W(Left)  formula (2)
     RR: aspect ratio of a right hand   H (Right): tallness (height) of the right hand   W (Right): broadness (width) of the right hand   RL: aspect ratio of a left hand   H (Left): tallness (height) of the left hand   W (Left): broadness (width) of the left hand
 
Here, the extracting section  211  may calculate the average value of RR and RL and use it as the aspect ratio.
   

       FIG. 4  is a schematic view illustrating an example of extracted hand areas. As illustrated in  FIG. 4 , from a captured image taken by the image capturing section  202 , hand areas are extracted by the extracting section  211  to calculate the aspect ratios of the left and right hand areas. 
     Here, in the example illustrated in  FIG. 4 , although the thumb of the left hand is not detected as it is behind the other fingers, it is not a problem because thumbs have little influence on a key push of an alphanumeric key. 
     The extracting section  211  also calculates threshold values used for determining a depth position, using aspect ratios R. The extracting section  211  calculates threshold values TH, for example, by multiplying predetermined coefficients by an aspect ratio R for each hand. The threshold values TH are obtained by the following formulas (3)-(6). TH is a generic symbol for the following threshold values.
 
 THUR=RR×X 1  formula (3)
 
THDR=RR×X2  formula (4)
 
 THUL=RL×X 1  formula (5)
 
 THDL=RL×X 2  formula (6)
     THUR: upper row (Up), right hand (Right) threshold value   THDR: lower row (Down), right hand (Right) threshold value   THUL: upper row (Up), left hand (Left) threshold value   THDL: lower row (Down), left hand (Left) threshold value   X 1 : a value less than 1 (X 1 &lt; 1 . 0 )   X 2 : a value greater than 1 (X 2 &gt; 1 . 0 )
 
where the origin is taken at the upper left corner of an image.
   

     Here, X 1  and X 2  are values proportionate to an amount of movement of fingers in the depth direction, which may be adjusted with a usability felt by a user, or may be set beforehand. If it is set beforehand, X 1  is set to, for example, 0.8, and X 2  is set to, for example, 1.2. 
     The extracting section  211  outputs the calculated threshold values TH to the depth position determining section  215 . Here, calculation of the threshold values may not be executed by the extracting section  211 , but by the depth position determining section  215  that has obtained the aspect ratios R from the extracting section  211 . 
     Referring to  FIG. 3  again, the reference line determining section  212  determines a reference position for determining a key pushdown move. The reference position is called a “reference pushdown line”. The reference line determining section  212  determines a reference pushdown line based on hand areas extracted by the extracting section  211 . 
     The reference line determining section  212  for example, may detect fingertips from the extracted hand areas and obtain an approximate line that connects the fingertip to set the line as a reference pushdown line. In this case, positions of fingers that are placed on a desk by a user are set as a reference pushdown line, which enables the user to operate on the desk as if it were a keyboard, and the user may feel an improved operability. 
       FIG. 5  is a schematic view illustrating an example of a virtual keyboard. Although three row of a QWERTY-type keyboard are illustrated in the example in  FIG. 5 , the number of rows is not limited to three, but may be four, five, or the like. 
     The reference line determining section  212  may set a reference pushdown line with positions that are taken by fingertips of a user when the user inputs with keys on the row closest to the user (for example, Z, X or the like in  FIG. 5 ) because these positions are located the highest (uppermost) in a two dimensional captured image. 
       FIG. 6  is a schematic view illustrating an example of a reference pushdown line. The reference pushdown line illustrated in  FIG. 6  has a distance M from the upper end of the image. In the example illustrated in  FIG. 6 , the reference pushdown line is set with positions of fingertips at home positions (assuming that the fingertips are placed on keys in the middle row illustrated in  FIG. 5 ). 
     Here, for a virtual keyboard with three rows as illustrated in  FIG. 5 , the reference line determining section  212  may detect a position of hands (M) when inputting with the middle row, multiply M by a coefficient a that is obtained with the aspect ratio R when inputting with the lower row, and use the multiplied value as a reference pushdown line. 
     Also, in the example illustrated in  FIG. 6 , although the same reference pushdown line is used for left and right hands, left and right hands may be set with respective reference pushdown lines. In this case, the reference line determining section  212  may obtain approximate lines by connecting fingertips of left and right hands, respectively. 
     The aspect ratio R (for the lower row) is a value that may represent a distance in the depth direction (closeness to a user), namely, a greater value of R makes the reference pushdown line set deeper in the depth direction, with which a key pushdown move in the lower row can be detected appropriately. 
     The reference line determining section  212  indicates the determined position of a reference pushdown line (for example, the distance M from the upper end of the image) to the determining section  213 . 
     The calibration procedure is executed as described above. The calibration procedure is a procedure for setting M used for a reference pushdown line required for a key input procedure, and threshold values TH. Here, if a user&#39;s identification information such as the fingerprint is associated with M and the threshold values TH and stored into the storage section  203 , the calibration procedure does not need to be executed every time. 
     (Key Input Procedure) 
     The image capturing section  202  captures movements of hands of a user to output an image to the extracting section  211 . The extracting section  211 , similarly to the calibration procedure, extracts hand areas from the image input from the image capturing section  202 . Also, the extracting section  211  calculates the aspect ratios R′ (current aspect ratios) of the extracted hand areas. 
     The extracting section  211  outputs the extracted hand areas to the determining section  213  and the lateral position determining section  214 , and outputs the calculated aspect ratios R′ to the depth position determining section  215 . 
     The determining section  213  illustrated in  FIG. 3  compares the reference pushdown line indicated by the reference line determining section  212  with the bottom part of the hand area extracted by the extracting section  211 , and determines a key pushdown move if the bottom part is at a position lower than the reference pushdown line. Here, “the bottom part is at a position lower than the reference pushdown line” means that the bottom part comes below the reference pushdown line in the image. 
     Here, if the coordinate system has the origin at the upper left position of the captured image and the vertical coordinate value increases in the downward direction, the determining section  213  determines a key pushdown move if the bottom part in the vertical direction is greater than the coordinate value of M. 
     The determining section  213  does not determines a key pushdown move if the vertical coordinate value of the bottom part is less than the coordinate value of M, namely, if the bottom part is not below the reference pushdown line. 
     The determining section  213  determines that a next key pushdown move takes place if a condition is satisfied that the bottom part moves above the reference pushdown line that has first been below the reference pushdown line. For example, the determining section  213  starts determining a next key pushdown move if the bottom part moves above the reference pushdown line that has first been below the reference pushdown line. 
       FIG. 7  is a schematic view illustrating an example of a key pushdown move. In the example illustrated in  FIG. 7 , the index finger of the right hand of a user comes below the reference pushdown line, which makes the determining section  213  determine the key pushdown move. In this case, the coordinate value of the index finger in the vertical direction is greater than M. 
     Once determining a key pushdown move, the determining section  213  indicates the key pushdown move to the lateral position determining section  214  and the depth position determining section  215 . 
     Referring to  FIG. 3  again, in response to an indication of a key pushdown move, the lateral position determining section  214  determines the lateral position based on the position of the bottom part of the hand area extracted by the extracting section  211 . 
     For example, the lateral position determining section  214  calculates a position of the bottom part relative to the width of the hand area. When inputting with the keys illustrated in  FIG. 5 , each hand is allocated five columns of keys because there are ten columns of keys in the lateral direction. 
     The lateral position determining section  214  divides the width of each of the hand areas by five, and allocates one key to each of the partitioned areas. The lateral position determining section  214  determines which one of the five partitioned areas includes the position of the bottom part. 
     Here, partitioning may be done evenly or done with ratios that take characteristics of the fingers of a user into account. The ratios that take characteristics of the fingers of a user into account depend on, for example, the positions and sizes of the fingers of the user, with which the ratio of the area between the index finger and the middle finger may be set wider than other areas. Also, partitioning may be done by a method specified by a user. 
       FIG. 8  is a schematic view illustrating an example of hand areas evenly partitioned. As illustrated in  FIG. 8 , the width of each of the hand areas is divided by five, and one column of keys is allocated to each of the partitioned areas. With this partitioning, the lateral position determining section  214  determines the lateral position of the pushing finger. 
     Once the lateral position of the pushing finger is determined, a candidate column of the input key is determined. The lateral position determining section  214  outputs the determined lateral position to the input key determining section  216 . With the example illustrated in  FIG. 7 , the lateral position determining section  214  determines that the area second to the leftmost for the right hand is the lateral position, and outputs the column of “u” to the input key determining section  216 . 
     Referring to  FIG. 3  again, the depth position determining section  215  obtains the threshold values TH calculated by the extracting section  211  during the calibration procedure. 
       FIG. 9  is a schematic view illustrating an example of threshold values TH. As illustrated in  FIG. 9 , the threshold values TH are used for determining the depth direction of a virtual keyboard. The virtual keyboard illustrated in  FIG. 9  has a front row from the user&#39;s viewpoint (the lower row in a captured image) including Z and N, a middle row from the user&#39;s viewpoint (the middle row in the captured image) including A and H, and a back row from the user&#39;s viewpoint (the upper row in the captured image) including Q and Y. 
     The depth position determining section  215  compares the aspect ratio R′ (current aspect ratio) of a hand area taken when a key pushdown move is determined by the determining section  213 , with the threshold values TH of the same hand with which the key pushdown move has been determined. For example, suppose that a key pushdown move with a right hand is determined. In this case, the depth position determining section  215  determines that the row of the key pushdown move is:
         the lower row if RR′&gt;THDR;   the middle row if THUR≦RR′≦THDR; or   the upper row if RR′&lt;THUR.       

     The reason why the row can be determined as above will be described with reference to  FIG. 10 . When inputting with a key in the upper row of the virtual keyboard, a finger is stretched in the direction towards the camera  104  in front, which makes the hand area take a form flattened in the vertical direction. Therefore, the aspect ratio (H (height)/W (width)) becomes smaller. 
       FIG. 10A  is a schematic view illustrating an example of a hand area when operating on the upper row. As illustrated in  FIG. 10A , the aspect ratio R′ becomes smaller. In the example illustrated in  FIG. 10A , the height (H) and width (W) are displayed only for the left hand. This is the same for  FIGS. 10B and 10C . 
     When inputting with a key in the middle row of the virtual keyboard, the positions are the same as the home positions, with which the aspect ratio R′ is the same as R when determining the reference pushdown line. 
       FIG. 10B  is a schematic view illustrating an example of a hand area when operating on the middle row. As illustrated in  FIG. 10B , the aspect ratio R′ for this case is the same as the aspect ratio R during the calibration. 
     When inputting with a key in the lower row of the virtual keyboard, the fingers moves towards the user (closer to the user), which makes the fingers form an upright shape. Therefore, the aspect ratio R′ becomes greater. 
       FIG. 10C  is a schematic view illustrating an example of a hand area when operating on the lower row. As illustrated in  FIG. 10C , the aspect ratio R′ becomes greater. 
     As illustrated in  FIGS. 10A-10C , the inventors discovered that the hand area of a user changes depending on the depth position of an input key (a key pushed down by the user). Based on this discovery, it is possible to estimate the position of a hand in the depth direction using the aspect ratio of the hand area of a user. 
     The depth position determining section  215  outputs the determined position in the depth direction (for example, one of the upper row (row for Q and Y), the middle row (row for A and H), and the lower row (row for Z and N)) to the input key determining section  216 . 
     The input key determining section  216  can uniquely determine the key (input key) pushed down by a user from the lateral position obtained from the lateral position determining section  214  and the depth position obtained from the depth position determining section  215 . 
       FIG. 11  is a schematic view illustrating an example of input key determination. In the example illustrated in  FIG. 11 , input is made with a left hand, the lateral position designates the column with “E”, and the depth position designates the row with “A” (middle row), and the input key is determined as “D”. 
     The input key determining section  216  stores the input command corresponding to the determined input key into the storage section  203 . In this case, the input command is a character code. The character codes stored into the storage section  203  may be output as a string on the display section  105 . 
     &lt;Operations&gt; 
     Next, operations of the information processing apparatus  10  will be described according to the first embodiment. 
     (Calibration Procedure) 
       FIG. 12  is a flowchart illustrating an example of the calibration procedure according to the first embodiment. At Step S 101  illustrated in  FIG. 12 , the image capturing section  202  captures an image of hands of a user. At this moment, for example, the hands of the user take the forms at the home positions. 
     At Step S 102 , the extracting section  211  extracts the hand area from the image captured by the image capturing section  202 . 
     At Step S 103 , the extracting section  211  calculates a reference aspect ratio R using the extracted hand area. The extracting section  211  may calculate threshold values TH using the aspect ratio R, and output them to the depth position determining section  215 . 
     At Step S 104 , the reference line determining section  212  calculates a reference pushdown line used for determining a key pushdown move based on the extracted hand area. The reference line determining section  212  calculates, for example, the distance M from the upper end of the image to set the position of the distance M from the upper end of the image as the reference pushdown line. This brings the calibration procedure to the end. 
     (Key Input Procedure) 
       FIG. 13  is a flowchart illustrating an example of a key input procedure according to the first embodiment. The key input procedure illustrated in  FIG. 13  is a procedure for a single frame. 
     At Step S 201 , the image capturing section  202  captures an image of hands of a user. In this case, the user, for example, performs key input operations on a desk that is likened to a keyboard. 
     At Step S 202 , the extracting section  211  extracts the hand area from the image captured by the image capturing section  202 . 
     At Step S 203 , the determining section  213  compares the bottom part of the extracted hand area and the reference pushdown line to determine whether the bottom part comes below the reference pushdown line. If it is determined that the bottom part is pushed down below the reference pushdown line (Step S 203 —YES), the procedure goes forward to Step S 204 , or if it is not determined that the bottom part is pushed down below the reference pushdown line (Step S 203 —NO), the next frame is going to be processed. 
     At Step S 204 , the lateral position determining section  214  determines the lateral position of the input key based on the position of the bottom part of the extracted hand area. For example, the lateral position is determined using the position of the bottom part relative to the width of the hand area. 
     At Step S 205 , the depth position determining section  215  compares the calculated aspect ratio R′ and the threshold values TH to determine the depth position of the input key. 
     At Step S 206 , the input key determining section  216  determines the input key from the determined lateral position and the determined depth position. This brings the key input procedure for a frame to the end. 
     (Hand Area Extracting Procedure) 
     Next, a hand area extracting procedure will be described. As described above, input key determination can be performed with better precision by extracting a hand area having a palm part removed. Therefore, a hand area extracting procedure with removal of a palm part will be described concretely using  FIG. 14 . 
       FIG. 14  is a flowchart illustrating an example of the hand area extracting procedure. At Step S 301 , the extracting section  211  converts RGB values of an image into HSV values that use hue, colorfulness, and luminosity. 
     At Step S 302 , the extracting section  211  extracts a flesh color from the HSV values. 
     At Step S 303 , the extracting section  211  determines whether the luminosity V of the extracted flesh color area is greater than a predetermined threshold value. The predetermined threshold value may be set to an appropriate value based on an experiment. 
     At Step S 304 , the extracting section  211  binarizes the flesh color area using the luminosity V. For example, the extracting section  211  sets “1” if the luminosity V is greater than the threshold value, or sets “0” if the luminosity V is less than the threshold value luminosity V. Then, removing a part of area set with “0”, the palm part can be removed from the flesh color area. The extracting section  211  may set the flesh color area having the palm part removed as the hand area. 
     In the procedure illustrated in  FIG. 14 , by extracting edges of fingers to remove a palm part so that the upper surface of the hand is extracted to be set as the hand area, an erroneous input by the palm part can be avoided. Also, by extracting only the upper surface of the hand, the palm part is prevented from being recognized as the bottom part of the hand area. 
     Here, although RGB values are converted into HSV values in the procedure illustrated in  FIG. 14 , RGB values may be converted into YUV values that represent brightness and color difference. In this case, a palm part can be deleted by determining with a threshold value using brightness Y. 
     Also, although determination with the threshold value using luminosity V (or brightness Y) is described in the procedure illustrated in  FIG. 14 , an opposite determination result may be obtained with the threshold value using luminosity V (or brightness Y) depending on characteristics of a flesh color of an individual person or a lighting environment. Further, the hand area extracting procedure may perform determination with threshold values taking hue H and colorfulness S (or color difference UV) into consideration. 
     As above, it is possible to perform key inputs based on three dimensional positions of fingers estimated from an image captured by a single camera in a single direction according to the first embodiment. Also, it is possible to reduce the cost of a device and to make the installation of an input device using a virtual keyboard easy because only one camera is required. 
     Also, according to the first embodiment, by deleting a palm part when extracting a hand area, an erroneous input by the palm part as the bottom part can be avoided and input precision with a virtual keyboard can be improved. 
     Also, a virtual keyboard according to the first embodiment can improve operability because the keys are determined following movements of hands, which expands the movable space of the hands of a user larger than the space available with a conventional technology. 
     Here, the display section  105  may display an image captured by the image capturing section  202 , or display a string corresponding to the character codes stored into the storage section  203 . Also, the display section  105  may display a captured image superposed with a virtual keyboard when displaying the captured image. The virtual keyboard may be superposed based on the position of the hand areas extracted by the extracting section  211 . 
     The information processing apparatus  10  may display on the screen, for example, how it recognizes an operation on the virtual keyboard. Alternatively, the information processing apparatus  10  may not display a screen for operations on the virtual keyboard if a user can perform touch typing. 
     The examples illustrated in  FIGS. 6, 7 , and  10  can be viewed as examples of captured images superposed with the virtual keyboard. Also, the display section  105  may display the virtual keyboard as a whole, or display only selected keys. 
     For example, the display section  105  may obtain a lateral position (key) determined by the lateral position determining section  214  or a depth position (key) determined by the depth position determining section  215  to highlight the key. 
     [Second Embodiment] 
     Next, an information processing apparatus  10  will be described according to a second embodiment. According to the second embodiment, instead of an estimation procedure for a lateral position, a finger estimation procedure is performed, and keys are arranged so that they correspond to the fingers estimated beforehand. 
     As the hardware of the information processing apparatus  10  and the functional configuration according to the second embodiment are the same as those in the first embodiment, the same numeral codes as in the first embodiment will be used for description. According to the second embodiment, the lateral position determination procedure by the lateral position determining section  214  differs from that of the first embodiment. 
     &lt;Functions&gt; 
     The lateral position determining section  214  of the information processing apparatus  10  extracts a color of nails to estimate fingers according to the second embodiment. Also, the lateral position determining section  214  may assign markers or the like to the fingers, and estimate the fingers by recognizing the markers by image processing. Also, the fingers may be estimated by characteristic values of the form of the fingers (a semicircular shape of a fingertip or the like). 
     The lateral position determining section  214  identifies a finger by estimating from the position of the finger in the hand area. For example, the leftmost finger in the left hand area is determined as the little finger, followed by the ring finger, the middle finger, and the index finger. 
     The lateral position determining section  214  for example, assigns “J” to the index finger of the right hand at the home position, “K” to the middle finger of the right hand, and “F” to the index finger of the left hand. This makes it possible to determine which key (lateral position) is pushed down in the lateral direction by determining which finger is pushed down. 
     Here, the index finger has two keys assigned. In this case, the lateral position determining section  214  can identify which one of the keys “J” and “H” is pushed down, for example, based on the amount of pushdown movement of the index finger of the right hand. 
     Specifically, the lateral position determining section  214  obtains the amount of movement in the lateral direction from the position of the index finger of the right hand when pushed down and the position of the index finger of the right hand in the previous frame of the image. With this amount of movement, it can be determined whether the finger has been pushed straight down from the home position, or pushed down obliquely. If the finger has been pushed straight down, the input key is determined as “J”, or if the finger has been pushed down obliquely, the input key is determined as “H”. The index finger of the left hand has substantially the same determination procedure applied. 
     The lateral position determining section  214  outputs the column of the determined key to the input key determining section  216 . The other functions are the same as in the first embodiment. 
     &lt;Operations&gt; 
     Operations of the information processing apparatus  10  will be described according to the second embodiment. The step differs from the first embodiment is Step S 204  illustrated in FIG. for determining an input key in the lateral direction. 
     According to the second embodiment, the lateral position determining section  214  estimates a finger in the hand area to determine which finger is pushed down at Step S 204 . The lateral position determining section  214  determines the input key (lateral position) in the lateral direction from the determined finger and the position of the finger if necessary. The other steps are the same as in the first embodiment. 
     As above, according to the second embodiment, it is possible to estimate which finger is pushed down, and to obtain the same effects as in the first embodiment. 
     Here, although the finger estimation procedure is performed for determining the lateral position according to the second embodiment, it may be combined with the lateral position determination procedure in the first embodiment. In this case, the lateral position determining section  214  determines the input key in the lateral direction based on a pushed finger and the position of the finger in the hand area. For example, if the index finger of the right hand is estimated to be the pushed finger, the input key is determined to be “J” or “H” depending on the position of the index finger of the right hand in the right hand area. 
     Also, the determining section  213  according to the second embodiment may use another method of determining a key pushdown move as follows. The determining section  213  makes comparison with the reference pushdown line for each of the estimated finger to determine that key pushes have been done for the fingers that are below the reference pushdown line. 
     By determining with the reference pushdown line for each finger, input can be done with multiple fingers at once, which makes an input operation faster than with the determination just using the bottom part. 
     [Third Embodiment] 
     Next, an information processing apparatus will be described according to a third embodiment. According to the third embodiment, multiple reference pushdown lines are provided to reduce erroneous determination of key pushes. 
     As the hardware of the information processing apparatus  10  and the functional configuration according to the third embodiment are the same as those in the first embodiment, the same numeral codes as in the first embodiment will be used for description. The reference line determining section  212  determines a reference pushdown line for each input row of a virtual keyboard according to the third embodiment. 
     &lt;Functions&gt; 
     The reference line determining section  212  of the information processing apparatus  10  determines a reference pushdown line for each input row of a virtual keyboard according to the third embodiment. For example, the calibration procedure illustrated in  FIG. 12  is executed for each of the input rows. For the virtual keyboard illustrated in  FIG. 5 , reference pushdown lines are determined for the upper row, middle row, and lower row, respectively. 
     The reference line determining section  212  indicates a reference pushdown line associated with each of the input rows of the virtual keyboard to the determining section  213 . The determining section  213  stores the reference pushdown lines associated with the respective input rows of the virtual keyboard. 
     The depth position determining section  215  determines the depth position based on an aspect ratio R of a hand area obtained from the extracting section  211 . In this case, for example, if it is determined that the current aspect ratio R′ indicates the upper row, the depth position determining section  215  indicates to the determining section  213  that the depth position is the upper row. 
     Obtaining the depth position from the depth position determining section  215 , the determining section  213  determines a key pushdown move using the reference pushdown line for the input row corresponding to the depth position. Determination of a key pushdown move is the same as in the first embodiment. The other functions are the same as in the first embodiment. 
     &lt;Operations&gt; 
     Next, operations of the information processing apparatus  10  will be described according to the third embodiment. The calibration procedure is executed for each of the input rows of the virtual keyboard according to the third embodiment. For example, following guidance on the display section  105 , a reference pushdown line is determined based on the hand area for one of the input rows. 
     (Key Input Procedure) 
       FIG. 15  is a flowchart illustrating an example of a key input procedure according to the third embodiment. The key input procedure illustrated in  FIG. 15  is a procedure for a single frame. 
     At Step  401 , the image capturing section  202  captures an image of hands of a user. In this case, the user, for example, performs key input operations on a desk that is likened to a keyboard. 
     At Step S 402 , the extracting section  211  extracts the hand area from the image captured by the image capturing section  202 . R′ is calculated from the extracted hand area. 
     At Step S 403 , the depth position determining section  215  compares a calculated aspect ratio R′ with threshold values TH to determine a input key depth position. 
     At Step S 404 , the determining section  213  compares the reference pushdown line corresponding to the determined depth position and the bottom part of the extracted hand area to determine whether the bottom part comes below the reference pushdown line. If it is determined that the bottom part is pushed down below the reference pushdown line (Step S 404 —YES), the procedure goes forward to Step S 405 , or if it is not determined that the bottom part is pushed down below the reference pushdown line (Step S 404 —NO), the next frame is going to be processed. 
     At Step S 405 , the lateral position determining section  214  determines the lateral position of the input key based on the position of the bottom part of the extracted hand area. For example, the lateral position is determined using the position of the bottom part relative to the width of the hand area. 
     At Step S 406 , the input key determining section  216  determines the input key from the determined lateral position and the determined depth position. This brings the key input procedure for a frame to the end. 
     As above, according to the third embodiment, it is possible to perform a key input depending on a three dimensional position of a finger in that the position is estimated based on a captured image taken by a camera in a single direction, and to determine a key pushdown move with improved precision. 
     [Modified Example] 
     Next, a modified example will be described. In the above embodiments, although a keyboard has been described as an example of an interface, it is possible to apply the above embodiments to menu selection buttons and pointing operations. 
     Also, in the above embodiments, although a virtual keyboard with three rows has been described as an example, the number of rows is not limited to three, but four, five, or the like. In these cases, three threshold values in the depth direction may be set for four input rows, and four threshold values may be set for five input rows. 
     In the modified example, it is possible to have a computer system execute the procedures described in the above embodiments by recording a program implementing the input control methods illustrated in  FIGS. 12-15  into a recording medium. 
     In this way, the input control procedures described in the embodiments may be implemented as a program to be executed by a computer. By installing the program in a computer from a server or the like and executing the program, the input control procedures described above can be implemented. 
     Also, it is possible to implement the above input control procedures by recording the program on a recording medium and having a computer or a portable terminal read the recording medium on which the program is recorded. 
     Here, various types of recording media can be used including a recording medium that records information optically, electrically, or magnetically such as a CD-ROM, a flexible disk, an optical magnetic disk and the like, and a semiconductor memory and the like that records information electrically such as a ROM, a flash memory, and the like. 
     The program executed on the information processing apparatus  10  in the embodiments has a modular configuration including the sections described above. In actual hardware, the control section  101  may read the program from the auxiliary storage section  103  and execute it so that one or more of the sections are loaded into the main memory section  102 , and one or more of the sections are generated in the main memory section  102 . 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.