Abstract:
A touch detection apparatus is provided, in which a touch panel is implemented with four surrounding edges. Three of the edges are embedded with retro-reflection materials. Light sources and pinholes are deployed on both corners of the touch panel, allowing reflections from the three edges to be projected on light sensors through the pinhole. The images projected on the light sensors are analyzed to determine coordinates of one or more contact points on the touch panel.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of Taiwan Patent Application No. 098134082, filed on Oct. 8, 2009, the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The disclosed embodiments relate to a touch screen, and more particularly to an apparatus and methods for sensing touch points by collecting reflection lights via a pinhole structure. 
     2. Description of the Related Art 
     Touch interfaces are broadly used in various electronic devices, such as handheld mobile apparatus or display panels. In current technologies, locations of points of contact are detected by using a resistive or capacitive sensor array, which may be stacked on an operation interface for detecting the contact points. However, as far as large display panels as concerned, the fabrication of sensor arrays has a high cost. In addition, some traditional touch interfaces adapt image sensing methods using photography equipment to determine whether the surface of a touch interface is touched. However, photography equipment requires light sensor components and lens costs. Moreover, in a multi-point touch situation, several sets of light sensor components and lenses must be installed and operated simultaneously to distinguishing the location of each contact point. Therefore, manufacturing cost for traditional touch detection is prohibitively expensive. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides a touch detection apparatus for detecting locations of touch points without using high cost photography equipment. An embodiment of a touch detection apparatus includes a touch panel encircled by four edges, wherein a first edge, a second edge and a third edge are embedded with retro-reflection materials. Light sources and pinholes are deployed on both corners of the touch panel according to an embodiment of the invention. Light sensors are disposed at outer edges of the touch panel and behind the pinholes for receiving images projected through the pinholes. The retro-reflection materials at the first edge, the second edge and the third edge are used to reflect the light from the light sources to the pinholes, so as to form images being projected on the light sensors. The coordinates of touch points on the touch panel are determined according to obstructed locations on the images. 
     A first light source and a first pinhole are disposed on the corner of the first edge and the fourth edge. The first light source emits a first light beam toward the second edge and the third edge to generate a first reflection light. In addition, a second light source and a second pinhole are disposed on the corner of the second edge and the fourth edge. The second light source emits a second light beam toward the first edge and the third edge to generate a second reflection light. A first light sensor module is disposed at the outer edge of the touch panel and separated from the first pinhole by a predetermined distance for detecting a first image projected on the first light sensor module by the first reflection light through the first pinhole. A second light sensor is disposed at the outer edge of the touch panel and separated from the second pinhole by the predetermined distance for detecting a second image projected on the second light sensor module by the second reflection light through the second pinhole. The first image and the second image are transmitted to a processor upon being received by the first light sensor module and the second light sensor module. 
     The processor performs an image analysis process according to the first image and the second image when the at least one object contacts the touch panel, so as to determine a coordinate of the touch point where the touch panel is contacted by at least one object. 
     Further, an embodiment of a touch point detection method is implemented based on the aforementioned touch detection apparatus. A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a block diagram illustrating a touch detection apparatus according to an embodiment of the invention; 
         FIG. 2  illustrates an embodiment of detecting a touch point according to the invention; 
         FIG. 3  illustrates an embodiment of simultaneously detecting two touch points according to the invention; 
         FIGS. 4   a  and  4   b  are two diagrams illustrating an embodiment of simultaneously detecting two touch points according to the invention; 
         FIG. 5  is a flow diagram illustrating an embodiment of detecting a touch point according to the invention; and 
         FIG. 6  is a flow diagram illustrating an embodiment of an embodiment of simultaneously detecting two touch points according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Compared to conventional touch detection techniques, an embodiment of the invention adapts a pinhole projection method for generating images, so as to reduce costs associated with lenses and photography equipment. Additionally, the arrangement of touch detection is also particularly arranged to facilitate the multi-point touch detection.  FIG. 1  is a block diagram illustrating a touch detection apparatus  100  according to an embodiment of the invention. The touch detection apparatus  100  comprises a touch panel  150  as an interface for receiving contact. The touch panel  150  is encircled by a first edge  110 , a second edge  120 , a third edge  130  and a fourth edge  140 . For description, the first edge  110  and the second edge  120  are respectively disposed on the right side and the left side of the touch panel  150 , as well as the third edge  130  and the fourth edge  140  is respectively disposed on the bottom side and the top side of the touch panel  150 . 
     Retro-reflection materials are disposed on the first, second, and third edges for reflecting an incoming light with any incident angles along with the original incident path. 
     The usage of retro-reflection materials may be implemented by accompanying various broadly existing technologies. Thus, detailed description is omitted for simplicity. A first pinhole  112  and a first light source  114  are disposed on the top right corner of the touch panel  150 , i.e., the cross corner of the first edge  110  and the fourth edge  140 . A first light beam emitted from the first light source  114  may have a field of view (FOV) of 90 degrees, including the entire ranges of the second edge  120  and the third edge  130 . The first pinhole  112  may collect a first reflection light reflected from the second edge  120  and the third edge  130 . A first light sensor module  116  is disposed at the outer edge of the touch panel  150  and separated from the first pinhole  112  by a predetermined distance. The first reflection light may be projected on the first light sensor module  116  through the first pinhole  112  to form a first image. Generally, if no obstruction exists among the first light source  114 , the second edge  120  and the third edge  130 , the first image represents the reflections from the second edge  120  and the third edge  130 . 
     Similarly, a second pinhole  122  and a second light source  124  are disposed on the top left corner of the touch panel  150 , i.e., the cross corner of the second edge  120  and the fourth edge  140 . A second light beam emitted from the second light source  124  may have a field of view (FOV) of 90 degrees, including the entire ranges of the first edge  110  and the third edge  130 . A second reflection light reflected from the first edge  110  and the third edge  130  may be collected by the second pinhole  122 . A second light sensor module  126  is disposed at the outer edge of the touch panel and separated from the second pinhole  122  by the predetermined distance for detecting a second image projected on the second light sensor module  126  by the second reflection light through the second pinhole  122 . 
     Specifically, when objects approach or contact the surface of the touch panel  150  on any locations, hue, brightness or texture variation may appear on the corresponding locations of the first image on the first light sensor module  116  and the second image on the second light sensor module  126 . For example, the first light source  114  and the second light source  124  may be specific light sources or light emitting diodes (LEDs) for generating specific beams, such as laser beams, infrared rays, or luminescence, and the first light sensor module  116  and the second light sensor module  126  are the corresponding receivers. Further, according to this embodiment, a visible ray may also be used as a light source, and the invention is not limited thereto. 
     In an embodiment of the invention, locations of touch points are determined by detecting the variation. In the touch detection apparatus  100 , a calculation unit  160  is coupled to the first light sensor module  116  and the second light sensor module  126  for receiving the first image and the second image, so as to perform image analyses. When at least one object contacts the touch panel  150 , the calculation unit  160  determines coordinates of touch points where the touch panel  150  is contacted by the at least one object according to the first image and the second image. The detailed description of determination will be given below. 
       FIG. 2  illustrates an embodiment of detecting a touch point P 1  according to the invention. For brevity of description, in  FIG. 2 , the touch panel  150  as shown in  FIG. 1  is simplified for illustrating light paths. In the embodiment of the invention, the first light sensor module  116  and the second light sensor module  126  may have the same length S for calculation purpose. The first sensor module  116  is diagonal to the fourth edge  140  by an angle of 45 degrees. The perpendicular bisector of the first light sensor module  116  is towards the first pinhole  112 , thus making both terminals of the first light sensor module  116  and the first pinhole  112  form an isosceles triangle. As a result, projected light beams from any locations of the touch panel  150  may be entirely received through the first pinhole  112 , especially the reflection light from the second edge  120  and the third edge  130 . Similarly, both terminals of the second light sensor module  126  and the second pinhole  122  also form an isosceles triangle for receiving the reflection light from the first edge  110  and the third edge  130 . 
     When an object, such as a finger or a touch pen, contacts the touch panel  150  on a first touch point P 1 , the reflection light from the second edge  120  and the third edge  130  are obstructed and unable to reach the first pinhole  112 , such that an obstructed point j 1  is projected on a location t 1  of the first light sensor module  116 . Similarly, the first touch point P 1  is projected as an obstructed point j 2  on a location t 2  of the second light sensor module  126  through the second pinhole  122 . Since the touch panel  150  is a flat plane, the first light sensor module  116  and the second light sensor module  126  are only required to detect one-dimensional line images for determining the location of the first touch point P 1 . Thus, the first light sensor module  116  and the second light sensor module  126  may be characterized by a specific line (i.e., one-dimensional) structure, instead of a pixel array with a large area. In this situation, only the variation of the specific light sources, such as gray levels, is required to be detected without fine hue gradation. Therefore, the cost is substantially lower than the conventional light sensor components. For example, the first image of the first light sensor module  116  and the second image of the second image of the second light sensor module  126  are displayed as line images with specific colors. 
     As shown in  FIG. 2 , the length of the first edge  110  and the second edge  120  equals the height of the touch panel  150 , indicated as H, as well as the length of the third edge  130  The fourth edge  140  also equals to the width of the touch panel  150 , indicated as W. According to an embodiment of the invention. the calculation unit  160  in  FIG. 1  performs an image analysis process including two steps of an angle conversion operation and a coordinate conversion operation for calculating a coordinate (x, y) of the first touch point P 1 . As shown in  FIG. 2 , the angle formed between a direction from the first touch point P 1  to the first pinhole  112  and the first edge  110  is defined as θ 1 , and the angle formed between a direction from the first touch point P 1  to the second pinhole  122  and the second edge  120  is defined as θ 2 . 
     Upon detecting the obstructed points j 1  and j 2  on the first light sensor module  116  and the second light sensor module  126 , the calculation unit  160  performs the angle conversion operation according to the following formula: 
     
       
         
           
             
               
                 
                   
                     
                       tan 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       θ 
                     
                     = 
                     
                       
                         t 
                         / 
                         s 
                       
                       
                         1 
                         - 
                         
                           t 
                           / 
                           s 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     wherein θ represents the angle formed between the direction from the pinhole to the obstructed point projected on the light sensor component and the vertical axis (such as the first edge  110  and the second edge  120 ), t represents the obstructed location of the obstructed point projected on the light sensor component, and S represents the length of the light sensor component. For example, it is assumed that the length of the first light sensor module  116  and the second light sensor module  126  are S, then the angles θ 1  and θ 2  as shown in  FIG. 2  may be obtained by replacing the obstructed locations of j 1  and j 2  into Formula (1): 
     
       
         
           
             
               
                 
                   
                     
                       tan 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         θ 
                         1 
                       
                     
                     = 
                     
                       
                         
                           t 
                           1 
                         
                         / 
                         s 
                       
                       
                         1 
                         - 
                         
                           
                             t 
                             1 
                           
                           / 
                           s 
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   and 
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   
                     tan 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       θ 
                       2 
                     
                   
                   = 
                   
                     
                       
                         
                           t 
                           2 
                         
                         / 
                         s 
                       
                       
                         1 
                         - 
                         
                           
                             t 
                             2 
                           
                           / 
                           s 
                         
                       
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     The aforementioned Formula (2) and Formula (3) are derived according to the arrangement for disposing the first light sensor module  116  and the second light sensor module  126  diagonal to the fourth edge  140  by the angle of 45 degrees. When the first light sensor module  116  and the second light sensor module  126  are arranged with different angles, the corresponding formula also differs. Specifically, the coordinate of each point on the touch panel  150  may have a one-to-one mapping on the first light sensor module  116  and the second light sensor module  126  through the first pinhole  112  and the second pinhole  122 . As a result, the coordinate (x, y) may be derived according to j 1  and j 2  with appropriate conversion formulas. 
     More specifically, according to embodiment of  FIG. 2 , since the first touch point P 1  locates at the intersection of two lines extended by the first pinhole  112  and the second pinhole  122 , the calculation unit  160  may further perform a conversion operation based on the obtained angles θ 1  and θ 2  and height H and width W of the touch panel  150 . The coordinate of the first touch point P 1  is accordingly obtained by use of simultaneous equations of trigonometric function. In this embodiment, omitting the derivation, the formula used for the conversion operation is indicated below: 
     
       
         
           
             
               
                 
                   
                     x 
                     = 
                     
                       
                         W 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         tan 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           θ 
                           2 
                         
                       
                       
                         ( 
                         
                           
                             tan 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               θ 
                               1 
                             
                           
                           + 
                           
                             tan 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               θ 
                               2 
                             
                           
                         
                         ) 
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   and 
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
             
               
                 
                   y 
                   = 
                   
                     H 
                     - 
                     
                       
                         W 
                         
                           ( 
                           
                             
                               tan 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 θ 
                                 1 
                               
                             
                             + 
                             
                               tan 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 θ 
                                 2 
                               
                             
                           
                           ) 
                         
                       
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     From Formula (4) and Formula (5), the coordinate of the first touch point P 1  is obtained by deriving the solution of the simultaneous equations involving two intersecting line segments respectively with the two angles θ 1  and θ 2 , and height and width of the touch panel  150 . The actual equations may differ from various locations of pinholes and various height and width of the touch panel  150 . Therefore, the embodiment of the invention is not limited to detailed calculation in Formula (4) and Formula (5). For brevity of the following description, the conversion function is generally denoted as:
 
 P ( x,y )= F (Θ a ,Θ b )  (6),
 
     wherein P(x, y) represents the coordinate of each point P, and F(Θ a , Θ b ) represents the calculation process of Formula (4) and Formula (5), i.e., the intersection associated with angles Θ a  and Θ b  is designated as a corresponding coordinate (x, y). For example, by inputting angles Θ a  and Θ b  into Formula (6), the coordinate of the first touch point P 1  is obtained as below:
 
 P 1( x,y )= F (θ 1 ,θ 2 )  (7).
 
     Further, the invention may be applicable to multipoint situations.  FIG. 3  illustrates an embodiment of simultaneously detecting a first touch point P 1  and a second touch point P 2  according to the invention. As the first reflection light of the second edge  120  and the third edge  130  is obstructed by the two touch points P 1  and P 2  on the touch panel  150 , two obstructed points K 1  and K 2  are generated on the first light sensor module  116 . Similarly, two obstructed points K 3  and K 4  are generated on the second light sensor module  126 . The obstructed locations of K 1 , K 2 , K 3 , and K 4  are respectively replaced in Formula (1) to obtain two angles θ 1  and θ 2  corresponding to the first pinhole  112 , as well as two angles φ 1  and φ 2  corresponding to the second pinhole  122 . Specifically, four lines respectively extending from the first pinhole  112  and the second pinhole  122  with angles θ 1 , θ 2 , φ 1  and φ 2  may generate four intersections P 1 , P 2 , Q 1 , and Q 2  on the touch panel  150  to derive the two touch points P 1  and P 2 . According to Formula (6), the coordinates of the four intersections are represented as:
 
 P 1( x,y )= F (θ 1 ,θ 2 )  (8),
 
 P 2( x,y )= F (φ 1 ,φ 2 )  (9),
 
 Q 1( x,y )= F (θ 2 ,φ 1 )  (10),
 
and
 
 Q 2( x,y )= F (θ 1 ,φ 2 )  (11),
 
     That is, two sets of possible solutions (P 1 , P 2 ) and (Q 1 , Q 2 ) may be generated by the calculation unit  160 . It is assumed that the first touch point is P 1 , and then the second touch point is determined to be P 2 . Moreover, it is assumed that the first touch point is Q 1 , and then the second touch point is determined to be Q 2 . Note that P 1 , P 2 , Q 1  and Q 2  are four coordinate candidates of the touch points since the actual solution is unable to be determined only by use of the four obstructed points K 1 , K 2 , K 3  and K 4 . For deriving the actual solution, the invention further provides the following method. 
       FIG. 4   a  is a diagram illustrating another embodiment of simultaneously detecting a first touch point P 1  and a second touch point P 2  according to the invention. 
     A third pinhole  132  is additionally disposed on the middle of the fourth edge  140  for capturing an additional image, so as to facilitate the first pinhole  112  and the second pinhole  122  to determine the correct solution of multipoint touch. The third pinhole  32  has a field of view of 180 degrees, and a left light sensor  136  and a right light sensor  146  are disposed at the outer edge of the fourth edge  140 . The left light sensor  136  and the right light sensor  146  have the same length and are disposed perpendicularly to each other, thus forming an isosceles triangle. The perpendicular bisectors of the left light sensor  136  and the right light sensor  146  are towards the third pinhole  132 . Accordingly, a field of view of 180 degrees is completely captured through the third pinhole  132 , i.e., reflection lights of the first edge  110 , the second edge  120  and the third edge  130  are collected and projected through the third pinhole  132 . Specifically, the left half portion of the touch panel  150  is within the field of view of the left light sensor  136  and the right half portion of the touch panel  150  is within the field of view of the right light sensor  146 . Thus, obstruction from a touch point at any location on the touch panel  150  can be detected through the third pinhole  132 . The arrangement of the light sensor modules is provided by disposing the left light sensor  136  and the right light sensor  146  perpendicularly to each other, however, other arrangements may be applicable for capturing 180-degree field of view, such as disposing a half-circle arc-shaped light sensor component centered at the third pinhole  132 . The invention is not limited thereto. 
     In this embodiment of  FIG. 4   a , assuming that two objects simultaneously touch the touch panel  150  on two touch points P 1  and P 2 , the obstructed points K 1  and K 2  are projected on the first light sensor module  116  and the obstructed points K 3  and K 4  are projected on the second light sensor module  126 . In addition, the first touch point P 1  located on the right half portion of the touch panel  150  is within the field of view of the right light sensor  146 , thus forming the obstructed point K 5  on the right light sensor  146 . Also, the second touch point P 2  located on the left half portion of the touch panel  150  forms the obstructed point K 6  on the left light sensor  136 . Upon detection by the left light sensor  136  and the right light sensor  146 , the calculation unit  160  obtains the angles θ 1 , θ 2 , φ 1 , and φ 2  respectively according to the obstructed points K 1  and K 2  on the first light sensor module  116  and the obstructed points K 3  and K 4  on the second light sensor module  126 . Then, two sets of possible solutions (P 1 , P 2 ) and (Q 1 , Q 2 ) are obtained based on Formula (8), (9), (10), and (11). Additionally, the obstructed point K 6  detected by the left light sensor  136  is replaced in Formula (1) to obtain an angle θ 3 . The line extended from the third pinhole  132  with respect to the angle θ 3  intersects the two lines extended from the second pinhole  122  with respect to the angles θ 2  and φ 2  at two points R 1  and P 2 , and the coordinates thereof are derived according to Formula (6):
 
 R 1( x,y )= F (θ 3 ,θ 2 )  (12)
 
and
 
 P 2( x,y )= F (θ 3 ,φ 2 )  (13).
 
     Furthermore, the obstructed point K 5  detected by the right light sensor  146  is replaced in Formula (1) to obtain an angle θ 4 . The line extended from the third pinhole  132  with respect to the angle θ 4  intersects the two lines extended from the first pinhole  112  with respect to θ 1  and φ 1  at two points R 2  and P 1 , and the coordinates thereof are derived according to Formula (6):
 
 R 2( x,y )= F (θ 4 ,φ 1 )  (14)
 
and
 
 P 1( x,y )= F (θ 1 ,θ 4 )  (15).
 
     Based on four solutions of Formula (12) to Formula (15), only two points R 1  and P 2  are determined according to the obstructed point K 6  on the left light sensor  136  and the obstructed points K 3  and K 4  on the second light sensor module  126 , and only two points R 2  and P 1  are determined according to the obstructed point K 5  on the right light sensor  146  and the obstructed points K 1  and K 2  on the first light sensor module  116 . Comparing Formula (12), (13), (14), (15) with the former Formula (8), (9), (10), (11), it is determined that (P 1 , P 2 ) is the intersection of the two sets of possible solution. As such, (P 1 , P 2 ) is determined to be the actual locations of touch points. 
     In some situations, the touch points P 1  and P 2  may possibly locate on the left half portion or right half portion. In this regard, the derivation remains the same without being affected by locations. For example,  FIG. 4   b  is a diagram illustrating another embodiment of simultaneous detection of a first touch point P 1  and a second touch point P 2  according to the invention. It is assumed that two objects simultaneously touch the touch panel  150  on the first touch point P 1  and the second touch point P 2 , the obstructed points K 1  and K 2  are projected on the first light sensor module  116  and the obstructed points K 3  and K 4  are projected on the second light sensor module  126 . Specifically, the touch points P 1  and P 2  located on the right half portion of the touch panel  150  are both within the field of view of the right light sensor  146 , thus forming the obstructed points K 5  and K 6  on the right light sensor  146 . In this regard, the calculation unit  160  obtains the angles θ 1 , θ 2 , φ 1 , and φ 2  respectively according to the obstructed points K 1  and K 2  on the first light sensor module  116  and the obstructed points K 3  and K 4  on the second light sensor module  126 . Then, two sets of possible solutions (P 1 , P 2 ) and (Q 1 , Q 2 ) are obtained based on Formula (8), (9), (10), and (11). Additionally, the obstructed points K 5  and K 6  detected by the left light sensor  136  are replaced in Formula (1) to obtain two angles θ 3  and φ 3 . Two lines respectively extended from the third pinhole  132  with respect to angles θ 3  and φ 3  intersect the two lines respectively extended from the first pinhole  112  with respect to angles θ 1  and φ 1  at four points P 1 , P 2 , R 1  and R 2 , and the coordinates thereof are derived according to Formula (6):
 
 P 1( x,y )= F (θ 1 ,θ 3 )  (16),
 
 P 2( x,y )= F (φ 1 ,φ3)  (17),
 
 R 1( x,y )= F (θ 3 ,φ 1 )  (18),
 
and
 
 R 2( x,y )= F (θ 1 ,φ3)  (19).
 
     Based on four solutions of Formula (16) to Formula (19), two sets of possible solutions (P 1 , P 2 ) and (R 1 , R 2 ) are determined according to the obstructed points K 5  and K 6  on the right light sensor  146  and the obstructed points K 1  and K 2  on the first light sensor module  116 . Next, comparing Formula (16), (17), (18), (19) with the former Formula (8), (9), (10), (11), it is determined that (P 1 , P 2 ) is the intersection of the two sets of possible solutions. As such, (P 1 , P 2 ) is determined to be the actual locations of touch points. 
     Similarly, several sets of possible solutions may be obtained by substituting angles θ 2  and φ 2  measured by the second light sensor module  126  and the angle φ 3  measured on the right light sensor  146  into Formula (6). Comparing formulas (8), (9), (10), (11), the intersection, i.e., (P 1 , P 2 ), is then determined. Furthermore, in some situations, coordinate candidates of the touch points outside the region of the touch panel  150  may be directly discarded to facilitate the determination of the actual coordinates of the touch points. 
     From the aforementioned description, the determination of multipoint touch is based on the simultaneous equations. The process of determining the locations of two touch points requires at least two simultaneous equations. It is sufficient for the first light sensor module  116  and the second light sensor module  126  to provide a first set of possible solutions. Further, a second set of possible solutions is provided by the left and right light sensor  136 / 146  and the first and second light sensor module  116 / 126 . The intersection of the first set and the second set of possible solutions is provided as the solution of the simultaneous equations. Similarly, if there are more than N touch points on the touch panel  150 , the location of each touch point is correspondingly determined by (N+1) pinholes with the same derivation and calculation process. 
       FIG. 5  is a flow diagram illustrating an embodiment of detecting a first touch point P 1  according to the invention. The process of  FIG. 2  may be simply represented as following steps. First, at step  501 , the touch panel  150  as shown in  FIG. 1  is activated. The first light source  114  and the second light source  124  emit light beams, and reflection lights of the first edge  110 , the second edge  120 , and the third edge  130  are projected on the first light sensor module  116  and the second light sensor module  126  through the first pinhole  112  and the second pinhole  122  based on pinhole projection. An object contacts the touch panel  150 , and the touch point is the first touch point P 1 . At step  503 , an obstructed point j 1  is detected at t 1  on the first light sensor module  116 . An angle θ 1  formed between a direction from the first touch point P 1  to the first pinhole  112  and the first edge  110  is calculated according to Formula (1). Moreover, at step  505 , an obstructed point j 2  is detected at t 2  on the second light sensor module  126 , so as to calculate an angle θ 2 . Following this, at step  507 , the angles θ 1  and θ 2  are replaced in the simultaneous equations depicted in Formula (4) and Formula (5), so as to obtain the coordinate of the first touch point P 1 . 
       FIG. 6  is a flow diagram illustrating an embodiment of an embodiment of simultaneous detection of a first touch point P 1  and a second touch point P 2  according to the invention. First, at step  601 , the touch panel  150  as shown in  FIG. 1  is activated for receiving multipoint contact. At step  603 , a first set of possible solutions is obtained based on the images detected by the first light sensor module  116  and the second light sensor module  126 , such as coordinate candidates as shown in Formula (8), (9), (10) and (11). At step  605 , a second set of possible solutions is obtained based on the solution of the simultaneous equations associated with the images detected by the first/second light sensor module  116 / 126  and the left/right light sensor  136 / 146 , such as coordinate candidates as shown in Formula (12), (13), (14) and (15). At step  607 , upon comparing the intersection of the first set and the second set of possible solutions, the actual coordinates of the touch points are accordingly determined, such as the coordinates of the first touch point P 1  and the second touch point P 2  as shown in Formula (13) and Formula (15). 
     The touch detection apparatus  100  according to the embodiments of the invention may applicable to handheld mobile devices, large projection screens, touch panels, or tablets. The arrangement of the touch panel, edges and pinholes may depend on application requirements, so as to perform the height, width and location adjustment. For example, the first light source  114  and the second light source  124  may be disposed everywhere without affecting the pinholes to receive reflection lights. 
     The area of the touch panel  150  may be smaller than or equal to the rectangular area encircled by the first edge  110 , the second edge  120 , the third edge  130  and the fourth edge  140 . The calculation unit  160  may consist of hardware circuits dedicated to analysis calculation of projected images, or a processor which could perform the calculation by executing operating systems and software. 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation to encompass all such modifications and similar arrangements.