Abstract:
Optical touch display system includes a light source, a reflector, an image sensor, and a processing device. The light source emits light to at least one object directly and emits light to the at least one object via the reflector at the same time. Then the image sensor receives light reflected from the at least one object directly and light reflected via the reflector simultaneously to form a set of imaging objects which have similar color parameters on an image. Then the processing device produces a set of still image parameters of the image objects such as gravity centers and border boundaries. Based on the still image parameters, the processing device determines the coordinates of the least one object on the optical touch display.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 12/817,172, filed on Jun. 16, 2010, entitled “Distance-measuring device, 3D image-sensing device, and optical touch system” and No. 12/842,045, filed on Jul. 23, 2010, entitled “Distance-measuring device of measuring distance according to variation of imaging location and calibrating method thereof”, the contents of which are incorporated herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to an optical touch display system, and more particularly, to an optical touch display system for multiple touch points. 
     2. Description of the Prior Art 
     Modern touch display technologies are already widely applied in electronic products of all kinds, e.g. Automated Teller Machine (ATM), handheld electronic devices and display devices. Generally, touch display technologies can be found in three types: resistive, capacitative and optical, wherein resistive and capacitative touch displays position an object via detecting variations in electric fields on surfaces of the touch displays when the object comes in contact with a sensing device. On the other hand, an optical touch display positions an object by detecting interruptions in light paths or light variations caused by the object moving on the surface of the touch display. 
     Since touch devices utilizing optical touch display technologies do not require special manufacturing processes or components, and also manufacturing costs are little affected by dimensions, optical touch technology is a more cost-effective solution than resistive and capacitative touch displays for larger-scale applications. To achieve a light-weight structure, optical touch display technologies often dispose image sensors at corners of touch screens and utilize triangulation to determine coordinates of a touch object from different angles. However, for two or more touch objects, measurement accuracy is reduced due to shadowing and obstruction of light paths, resulting in less accurate or incorrect coordinates (ghost coordinates), causing inconvenience for various applications. 
     SUMMARY OF THE INVENTION 
     The present invention discloses an optical touch display system. The optical touch display system comprises a touch region; a light source, disposed on a periphery of the touch region, the light source positioned at least partially above the touch region, such that light rays emitted from the light source may traverse the touch region; a reflector, disposed on at least a part of the periphery of the touch region, for reflecting the light rays emitted from the light source and generating a mirrored image of the touch region; an image sensor, disposed above the light source, for receiving light rays of the light source, reflected from a set of touch points on the touch region and the reflector, and generating a two-dimensional image accordingly; wherein the two-dimensional image comprises a set of optical images, the set of optical images comprising a set of real images corresponding to the set of touch points, and a set of virtual images corresponding to the set of touch points, generated by the light rays from the light source reflected by the reflector; and a processing device, for generating a set of output coordinates corresponding to the set of touch points according to positions of the set of real images and the set of virtual images in the two-dimensional image. 
     The present invention further discloses an optical touch display system. The optical touch display system comprises a touch region; a light source, on a periphery of the touch region, the light source positioned at least partially above the touch region, such that light rays emitted from the light source may traverse the touch region; an image sensor, disposed above the light source, for receiving light rays of the light source, reflected from a set of touch points on the touch region, and generating a two-dimensional image accordingly; wherein the two-dimensional image comprises a set of optical images corresponding to the set of touch points; a distance measurement device, connected to the light source and the image sensor, for controlling the light source and the image sensor, and generating a set of image distances corresponding to the set of optical images according to coordinates of the set of optical images in the two-dimensional image along a first direction; an angle measurement device, connected to the image sensor, for generating a set of image angles corresponding to the set of optical images according to coordinates of the set of optical images in the two-dimensional image along a second direction; and a processor, for generating a set of output coordinates according to the set of image distances and the set of image angles. 
     The present invention further discloses an optical touch display system. The optical touch display system comprises a touch region; a light source, disposed on a periphery of the touch region, the light source positioned at least partially above the touch region, such that light rays emitted from the light source may traverse the touch region; a first image sensor, disposed above the light source, for receiving light rays of the light source, reflected from a set of touch points on the touch region, and generating a first two-dimensional image accordingly; wherein the first two-dimensional image comprises a first set of real images corresponding to the set of touch points; a second image sensor, disposed on the periphery of the touch region, for receiving light rays of the light source, reflected from the set of touch points on the touch region, and generating a second two-dimensional image accordingly; wherein the second two-dimensional image comprises a second set of real images corresponding to the set of touch points; a distance measurement device, connected to the light source and the first image sensor, for controlling the first image sensor and the light source, and generating a first set of image distances corresponding to the first set of real images according to coordinates of the first set of real images in the two-dimensional image along a first direction; and a processor, for generating a first set of real-image lines according to the first set of real images and a position of the first image sensor in the first two-dimensional image, and generating a second set of real-image lines according to the second set of real images and a position of the second image sensor in the second two-dimensional image, and the processing device generates a set of candidate coordinates corresponding to the set of touch points according to the first set of real-image lines and the second set of real-image lines, and generates a set of output coordinates corresponding to the set of touch points according to the set of candidate coordinates and the first set of image distances. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an optical touch display system according to a first embodiment of the present invention. 
         FIG. 2  is a schematic diagram of the optical touch display system during a calibration stage according to the first embodiment of the present invention. 
         FIG. 3  is a schematic diagram the optical touch display system under normal operation according to the first embodiment of the present invention. 
         FIG. 4  is a side-view schematic diagram of the optical touch display system according to the first embodiment of the present invention. 
         FIG. 5  is a top-view schematic diagram of the optical touch display system according to the first embodiment of the present invention. 
         FIG. 6  is a schematic diagram of an optical touch display system according to a second embodiment of the present invention. 
         FIG. 7  is a flowchart of a process of the optical touch display system detecting a touch point position according to the second embodiment of the present invention. 
         FIGS. 8-12  are schematic diagrams illustrating the process shown in  FIG. 7 . 
         FIG. 13  is a schematic diagram of an optical touch display system according to a third embodiment of the present invention. 
         FIG. 14  is a flowchart of a process of the optical touch display system detecting a touch point position according to the third embodiment of the present invention. 
         FIG. 15  is a schematic diagram illustrating the process shown in  FIG. 14 . 
         FIGS. 16 and 17  are schematic diagrams illustrating structure and operation of a distance measurement device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1 , which is a schematic diagram of an optical touch display system  100  according to a first embodiment of the present invention. The optical touch display system  100  includes an image sensor  101 , a light source  102 , a touch region  103 , a light absorption component  104 , and a processing device  120 . The processing device  120  includes a distance measurement device  105 , an angle measurement device  106 , and a processor  107 . The optical touch display system  100  is capable of detecting multiple touch points. Moreover, the distance measurement device  105  further controls the image sensor  101  and the light source  102  via a control signal S C . In  FIG. 1 , only two touch points O 1 , O 2  are shown for illustrative purposes. Moreover, relative positions of components in  FIG. 1  are shown for illustration, and in reality the components may be disposed differently. In reality, a lens LN is disposed on a sensing side of the image sensor  101  in the optical touch display system  100 , such that all incident light rays to the image sensor  101  pass through the lens LN. However, the lens LN is omitted from  FIG. 1  for simplicity. 
     Preferably, the touch region  103  is set to a rectangle, and the light absorption component  104  is disposed on a periphery of the touch region  103 , for absorbing light rays of the light source  102  such that light rays of the light source  102  are not reflected back to the image sensor  101 . However, the touch region  103  can also be set to a trapezoid, or other polygonal shapes, according to user requirements. The light source  102  is disposed on the periphery of the touch region  103 ; preferably, the light source  102  is positioned at least partially above a corner of the touch region touch region  103 , such that light rays emitted from the light source  102  may traverse the touch region  103 . The image sensor  101  is disposed close to the light source  102 ; preferably, the image sensor  101  is disposed above the light source  102 . Moreover, the light source  102  may be a two-dimensional light source, including a linear light source and a light source conversion device, wherein the linear light source is generated via a laser diode or a Light Emitting Diode (LED); the light source conversion device converts the linear light source to the two-dimensional light source, to generate light rays on the touch region  103 ; the light source conversion device may be a cylindrical lens, a Diffractive Optical Element (DOE) or a MEMS micro mirror module. 
     The image sensor  101  contains a light sensing array constituted from M columns and N rows of sensing units, and generates a two-dimensional image F with a resolution of M by N. More specifically, in Cartesian coordinates, the two-dimensional image F has a resolution of M along an X-axis and a resolution of N along a Y-axis. 
     In one embodiment, the present invention employs a polar coordinate system for the touch region  103 . As shown in  FIG. 1 , the origin (0,0) of the polar coordinate system is defined as a top-left corner of the touch region  103 , and the polar axis is defined as a top boundary of the touch region  103 . Preferably, the image sensor  101  is disposed at the top-left corner of the touch region, i.e. polar coordinates of the image sensor  101  is also the origin (0,0); the light source  102  is also disposed at the top-left corner of the touch region, i.e. polar coordinates of the light source  102  is also the origin (0,0). Therefore, a position of an object on the touch region  103  is represented by a distance R from the top-left corner of the touch region  103 , and an angle θ from the top boundary of the touch region  103 . 
     The distance measurement device  105  and the angle measurement device  106  measures an image distance and image angle of the touch point according to positions of an optical image generated by light rays reflected from the touch point in the two-dimensional image F. More specifically, the distance measurement device  105  calculates the distance of the touch point according to a position of the optical image in the two-dimensional image F along the Y-axis; the angle measurement device  106  calculates the angle of the touch point according to a position of the optical image in the two-dimensional image F along the X-axis. The processing device  107  further outputs the position of the touch point (in distance and angle) according to information obtained by the distance measurement device  105  and the angle measurement device  106 . 
     Please refer to  FIG. 2 , which is a schematic diagram illustrating the optical touch display system  100  during a calibration stage. Before starting to detect the position of the touch point, the optical touch display system  100  may first undergo a calibration stage. The following illustrates operations of the optical touch display system  100  of the present invention during the calibration stage. For the same illustrative purposes, the lens LN is omitted from  FIG. 2 . 
     During the calibration stage, calibration objects P 1 , P 2 , P 3 , P 4  can be disposed at each of four corners of the touch region  103 , corresponding to coordinates (R P1 , θ P1 ), (R P2 , θ P2 ), (R P3 , θ P3 ), (R P4 , θ P4 ), respectively. The light source  102  emits light rays at the calibration objects P 1 , P 2 , P 3 , and P 4 , respectively; the calibration objects P 1 , P 2 , P 3 , and P 4  reflect the light rays from the light source  102  to the image sensor  101 . Here, it is assumed that the calibration objects P 1 , P 2 , P 3 , P 4  respectively form images on the sensing units CS (M, 0) , CS (M,N) , CS (0,N) , CS (0,0)  (assumed for illustrative purposes only, and may differ in reality). In other words, coordinates of optical images I P1 , I P2 , I P3 , I P4  corresponding to the calibration objects P 1 , P 2 , P 3 , P 4  on the two-dimensional image F are (M,0), (M,N), (0,N), (0,0), respectively. Since that the calibration objects P 1 ˜P 4  are disposed at corners of the touch region, and that a length and width of the touch region  103  are both known, and providing that the origin (0,0) is defined as the top-left corner of the touch region, it follows that (R P1 , θ P1 ), (R P2 , θ P2 ), (R P3 , θ P3 ), (R P4 , θ P4 ) may be mathematically determined. For example, assuming the length and width of the touch region  103  are R L  and W L , then (R P1 , θ P1 ), (R P2 , θ P2 ), (R P3 , θ P3 ), (R P4 , θ P4 ) may be expressed (0,0), (R L ,0), ((R L   2 +W L   2 ) 1/2 , tan −1 (W L /R L )), (W L , 90°), respectively. As such, in the case of the calibration objects P 3  and P 4 , the distance measurement device  105  can know that a distance difference of N along the Y-axis in the two-dimensional image F is equivalent to a distance difference of W L  in actual space. Thus, a distance of an object from the origin on the touch region  103  may be derived, via interpolation, from a position of a corresponding optical image along the Y-axis in the two-dimensional image F. In the case of the calibration objects P 1  and P 3 , the angle measurement device  106  knows that a distance difference of M along the X-axis in the two-dimensional image F is equivalent to an actual angle difference of 90°. Thus, an angle of an object from the polar axis on the touch region  103  may be derived from a position of a corresponding optical image along the X-axis in the two-dimensional image F, via interpolation. Moreover, in the above-mentioned calibration method, different variations according to user requirements are possible, e.g. different positions or a different quantity of the calibration objects, etc. 
     Please refer to  FIG. 3 , which is a schematic diagram of the optical touch display system  100  during normal operation according to the present invention. During normal operation, the light source  102  emits the light rays to the touch point O 1 ; the touch point O 1  reflects the light rays emitted from the light source  102  back to the image sensor  101 , and an image is formed on the sensing unit CS (X1,Y1) . In other words, the touch point O 1  corresponds to an optical image I O1  with coordinates (X 1 ,Y 1 ) in the two-dimensional image F. Since the coordinate relationship between the touch region  103  and the two-dimensional image F can be known by the distance measurement device  105  and the angle measurement device  106  after the calibration stage, it is possible to calculate that a position of the touch point O 1  in the touch region  103  is at (R O1 , θ O1 ). A position of the touch point O 2  may be calculated in a way similarly to the touch point O 1 , and not further described herein. 
     Please refer to  FIG. 4 , which is a side-view schematic diagram of the optical touch display system  100 .  FIG. 4  illustrates how the distance measurement device  105  measures the distance R, and uses the calibration objects P 1 , P 2  and the touch point O T  as an example. Furthermore, the lens LN shown in  FIG. 4  illustrates that all inflecting light rays of the image sensor  101  pass through the lens LN, therefore resulting in image positions as shown in  FIG. 4 . It may be assumed that the calibration objects P 1  and P 2  are spaced apart by a known distance R L , and correspond to optical images I P1  and I P2  in the two-dimensional image F, with coordinates (M,N) and (M,0), respectively. It follows that, R OT , a distance of the touch point O T  to be detected by the distance measurement device  105 , may be derived from a position of an optical image I OT  (corresponding to the touch point O T ) relative to the optical images I P1 , I P2  along the Y-axis in the two-dimensional image F. More specifically, suppose the optical image I OT  is at (X T , Y T ), then the distance R OT  may be expressed as follows: R OT =(Y T /N)×R L . 
     Please refer to  FIG. 5 , which is a top-view of the optical touch display system  100 .  FIG. 5  illustrates how the angle measurement device  106  measures the angle θ, using the calibration objects P 2 , P 3  as an example. Assume that an angle Θ P3  between the calibration objects P 2  and P 3  is known (e.g. tan −1 (W L /R L )), and that the calibration objects P 2  and P 3  correspond to optical images I P2  and I P3 , at positions (M,N) and (0,N), respectively. It follows that the angle θ OT  of the touch point O T  to be detected by the angle measurement device  106  may be derived from the position of the optical image I OT  relative to the optical images I P2  and I P3  along the X-axis in the two-dimensional image F. More specifically, suppose the optical image I OT  is at (X T , Y T ), then the angle θ OT  may be expressed by the following: θ OT =(X T /M)×θ P3 . 
     Please refer to  FIG. 6 , which is a schematic diagram of an optical touch display system  600  according to a second embodiment of the present invention. Compared with the optical touch display system  100 , the optical touch display system  600  is configured with an extra reflector  108 , for enhancing accuracy of determining positions of the touch points. Furthermore, the processing device  120  of the optical touch display system  600  may optionally include a real image determination device  170 . In the following, it is assumed that it is known whether the optical images in the two-dimensional image F are real images or not. Moreover, those skilled in the art may derive other cases according to the aforementioned relationship between positions of an object in the touch region and its corresponding optical image in the two-dimensional image. Therefore, for illustrative purposes, the following mainly describes positions of objects within the touch region. 
     Please refer to  FIG. 7 , which is a flowchart of a process illustrating the optical touch display system  600  detecting the position of the touch point. For simplicity, the following describes a case with two touch points O 1 , O 2 . Moreover, steps disclosed in  FIG. 7  merely serve illustrative purposes. In practice, operations do not need to follow the steps as disclosed in  FIG. 7 . The steps of the process are as follows: 
     Step  701 : The light source  102  emits light rays, and generate optical images I O1 , I O2 , I O1J , I O2J  in the two-dimensional image F via reflections of the touch points O 1 , O 2 , and the reflector, wherein I O1J  and I O2J  are mirrored images (virtual images) of the touch points O 1  and O 2 , respectively; refer to  FIG. 8 ; dashed-lined areas in  FIG. 8  represent mirrored images produced by the reflector  108  reflecting the light rays of the light source  102 , wherein the touch points O 1 , O 2  correspond to mirrored images O 1J  and O 2J , respectively. Therefore, the image sensor  101  sees four optical images I O1 , I O2 , I O1J  and I O2J , wherein O 1J  and O 2J  are virtual images, as shown by the two-dimensional image F in  FIG. 8 . 
     Step  702 : The angle measurement device  106  generates image angles θ O1 , θ O2 , θ O1J , and θ O2J  according to positions of the optical images I O1 , I O2 , I O1J , and I O2J  along the X-axis in the two-dimensional image F. Please refer to  FIG. 9A . 
     Step  703 : Using the light source  102  as an origin, the processing device  107  generates real-image lines SL O1  and SL O2 , and virtual-image lines SL O1J , SL O2J  according to the image angles θ O1 , θ O2 , θ O1J , θ O2J , respectively; please refer to  FIG. 9B . 
     Step  704 : The processing device  107  calculates intersection points G 1 , G 2  at which the virtual-image lines SL O1J  and S LO2J  intersect a plane on which the reflector  108  is disposed; the processing device  107  generates virtual-image lines SL G1  and SL G2  according to a mirrored image  101   J  of the image sensor  101  (or a mirrored image  102   J  of the light source  102 ), and the intersection points G 1 , G 2 ; please refer to  FIG. 10 . 
     Step  705 : The processing device  107  calculates and generates four candidate coordinates O C1 , O C2 , O C3  and O C4  according to the real-image lines SL O1 , SL O2  and the virtual-image lines SL G1 , SL G2 ; please refer to  FIG. 11 . 
     Step  706 : The distance measurement device  105  generates image distances R O1 , R O2  according to positions of the optical images I O1 , I O2  along the Y-axis in the two-dimensional image F; please refer to  FIG. 12A . 
     Step  707 : The processing device  107  selects a candidate coordinate on the real-image line SL O1  having a minimum deviation from the image distance R O1  as an output coordinate for the touch point O 1 ; please refer to  FIG. 12B ; the processing device  107  selects a candidate coordinate on the real-image line SL O2  having a minimum deviation from the image distance R O2 , as an output coordinate for the touch point O 2 ; please refer to  FIG. 12B . 
     As can be seen from the above, the optical touch display system  600  may first measure the image angle via the image sensor  101  and the reflector  108 , then determine the coordinate with minimum deviation within the candidate coordinates according to the distance measured by the distance measurement device  105 , and then output the coordinate as the final output coordinate of the touch point. 
     Moreover, the image distance measured by the measurement device  105  can only be used in steps  707 ,  708  to determine the output coordinates within the candidate coordinates; therefore, extremely high measurement accuracy for the image distance is not required. In reality, the output coordinates of the touch points may still be calculated and decided by the processing device  107  using the measured angle. 
     Furthermore, the real image determination device  170  determines whether the optical images on the image sensor  101  corresponding to the optical images in the touch region are real images or virtual images. More specifically, the real image determination device  170  is capable of determining whether an optical image X is a real image, according to whether a measured image distance R X  and image angle θ X  of the optical image X satisfies a predefined relationship. For example, the optical image X is determined to be a real image if the predefined relationship between the image distance R X  and the image angle θ X  is satisfied, such that coordinates of the optical image X fall within a range of the touch region  103 . Conversely, the optical image X is determined as a virtual image. 
     Please refer to  FIG. 13 , which is a schematic diagram of an optical touch display system  1300  according a third embodiment of the present invention. Compared with the optical touch display system  100 , the optical touch display system  1300  is configured with an extra image sensor  109  with functionalities similar to that of the reflector  108 , mainly for enhancing accuracy of determining the positions of the touch points. Preferably, the image sensor  109  may be disposed at the top-right corner of the touch region  103 . Operations of the optical touch display system  1300  are similar to that of the optical touch display system  600 , and details of which are provided in the following. 
     Please refer to  FIGS. 14 and 15 .  FIG. 14  illustrates a process through which the optical touch display system  1300  detects a position of a touch point.  FIG. 15  is a schematic diagram illustrating the process shown in  FIG. 14 . Moreover, steps of the process disclosed in  FIG. 14  merely serve illustrative purposes. In practice, operations do not need to follow the process disclosed in  FIG. 14 . The steps of the process are as follows: 
     Step  1401 : The light source  102  emits light rays, which are reflected by the touch points O 1  and O 2 ; optical images I O11 , I O21  are generated in the two-dimensional image F 1  sensed by the image sensor  101 , and optical images I O19 , I O29  are also generated in the two-dimensional image F 2  sensed by the image sensor  109 . 
     Step  1402 : The angle measurement device  106  generates image angles θ O11 , θ O21 , θ O19 , and θ O29  according to positions of the optical images I O11 , I O21  along the X-axis in the two-dimensional image F 1 , and according to positions of the optical images I O19 , I O29  along the X-axis direction in the two-dimensional image F 2 , respectively; note that the image sensor  109  is the origin for the angles θ O19 , θ O29 . 
     Step  1403 : Using position of the image sensor  101  as origin, the processing device  107  generates real-image lines SL O11  and SL O21 , according to the image angles θ O11 , θ O21 , respectively; and then using position of the image sensor  109  as an origin, the processing device  107  generates real-image lines SL O19  and SL O29  according to the image angles θ O19 , θ O29 , respectively. 
     Step  1404 : Next, the processor  107  calculates intersections of the real-image lines SL O11 , SL O21 , SL O19 , SL O29  and virtual-image lines SL G1 , SL G2 , to calculate and generate four candidate coordinates O C1 , O C2 , O C3  and O C4 . 
     Step  1405 : The distance measurement device  105  generates image distances R O11 , R O21  according to positions of the optical images I O11 , I O21  along the Y-axis in the two-dimensional image F 1 . 
     Step  1406 : The processor  107  selects a candidate coordinate on the real-image line SL O11  having minimum deviation from the image distance R O11  as an output coordinate for the touch point O 1 ; the processor  107  selects a candidate coordinate on the real-image line SL O21  having minimum deviation from the image distance R O21  as an output coordinate for the touch point O 2 . 
     As can be seen from the above, the optical touch display system  1300  may first measure the image angles via the image sensors  101  and  109 , then determine the coordinate within the candidate coordinates with minimum deviation according to the distance measured by the distance measurement device  105 , and then output the coordinate as the final output coordinate of the touch point. 
     Moreover, the image distance measured by the measurement device  105  can only be used in steps  1407 ,  1408  to determine the output coordinates within the candidate coordinates; therefore, extremely high measurement accuracy for the image distance is not required. In reality, the output coordinates of the touch points may still be calculated and decided by the processing device  107  using the measured angles. 
     Please refer to  FIGS. 16 and 17 , which are schematic diagrams illustrating structure and operations of the distance measurement device  105  according to the present invention. Disposed as shown in  FIG. 1 , the distance measurement device  105  measures the image distance R O1  between the touch point O 1  and the light source  102 . The distance measurement device  105  includes a lighting/sensing control circuit  110  and a distance calculation circuit  140 . The lighting/sensing control circuit  110  generates a control signal S C  to control the light source  102  and the image sensor  101 . Connections of internal components in the distance measurement device  105  are shown in  FIG. 1 , and not reiterated herein. Moreover, to enhance accuracy, it is possible to further dispose lenses LEN 1  and LEN 2  in front of the image sensor  101  and the light source  102 , respectively. 
     The control signal S C  generated by the lighting/sensing control circuit  110  includes a light pulse signal S LD , a shutter pulse signal S ST , phase signal S P , read signal S RE , and known distance signal S D . Distance measurement performed by the distance measurement device  105  may be divided into two stages: 1. Distance sensing stage; and 2. Noise sensing stage. During the distance sensing stage, the lighting/sensing control circuit  110  of the distance measurement device  105  simultaneously generates the light pulse signal S LD  representing “lit” and the shutter pulse signal S ST  representing “open”, both with a pulse width of T C ; then the lighting/sensing control circuit  110  simultaneously generates the read signal S RE  representing “read” and the phase signal Sp representing “sum”, both with a pulse width of T R . When the distance measurement device  105  is in the noise sensing stage, the lighting/sensing control circuit  110  generate the shutter pulse signal S ST  representing “open” and simultaneously, the light pulse signal S LD  representing “unlit”, and the shutter pulse signal has a pulse width of T C ; then the lighting/sensing control circuit  110  simultaneously generates the read signal S RE  representing “read” and the phase signal Sp representing “noise”, both with a pulse width of T R . 
     The light source  102  is controlled by the lighting/sensing control circuit  110 , and used for emitting a detecting light ray L ID  to the touch point O 1  according to the light pulse signal S LD , such that the touch point O 1  generates a reflecting light ray L RD . More specifically, when the light pulse signal S LD  represents “lit”, the light source  102  emits the detection light ray L ID  to the touch point O 1 ; when the light pulse signal S LD  represents “unlit”, the light source  102  does not emit the detection light ray L ID . 
     Take a column of the image sensor  101  as an example, e.g. a Q-th sensing column CS Q  includes N sensing units CS (Q,1) ˜CS (Q,N)  set side-by-side, each sensing unit having a height equal to a pixel height H PIX , i.e. the N sensing units CS (Q,1) ˜CS (Q,N)  set side-by-side measure a total width of N×H Pix . The sensing units CS (Q,1) ˜CS (Q,N)  are for detecting an energy of the light rays converged by the lens LEN 1  according to the shutter pulse signal S ST . More specifically, when the shutter pulse signal S ST  represents “open”, the sensing units CS (Q,1) ˜CS (Q,N)  detect the energy of the light rays converged by the lens LEN 1  (e.g. background light ray L B  or reflected light ray L RD ) to generate the light sensing signal accordingly; when the shutter pulse signal S ST  represents “shut”, the sensing units CS (Q,1) ˜CS (Q,N)  do not detect the energy of the light rays converged by the lens LEN 1 . For example, when the shutter pulse signal S ST  represents “open”, the sensing unit CS (Q,1)  senses the energy of the light rays converged by the lens LEN 1  to generate a light sensing signal S LS1  accordingly; the sensing unit CS (Q,2)  senses the energy of the light rays converged by the lens LEN 1  to generate a light sensing signal S LS2 ; similarly, the sensing unit CS (Q,N)  senses the energy of the light rays converged by the lens LEN 1  to generate light sensing signal S LSN . Moreover, when the read signal S RE  represents “read”, the sensing units CS (Q,1) ˜CS (Q,N)  output the light sensing signals S LS1 ˜S LSN , respectively, forming the image signal for the Q-th column of the two-dimensional image F. 
     The distance calculation circuit  140  includes a plurality of storage units, used for storing the light sensing signals S LS1 ˜S LSN  outputted by the sensing units CS (Q,1) ˜CS (Q,N) , respectively, and for setting properties of the received light sensing signals according to the phase signal S P . In this embodiment, the distance calculation circuit  140  includes N storage units M 1 ˜M N  as an example. When the phase signal Sp represents “sum”, the storage units M 1 ˜M N  set the received light sensing signals S LS1 ˜S LSN  as positive, i.e. the receive light sensing signals S LS1 ˜S LSN  represent “sum” according to the phase signal S P , and are marked as positive light sensing signals S LS1+ ˜S LSN+ ; when the phase signal S P  represents “noise”, the storage units M 1 ˜M N  set the received light sensing signals S LS1 ˜S LSN  as negative, i.e. the receive light sensing signals S LS1 ˜S LSN  represent “noise” according to the phase signal S P  and are marked as negative light sensing signals S LS1− ˜S LSN− . The distance calculation circuit  140  can calculate the image distance R O1  according to the positive light sensing signals S LS1+ ˜S LSN+  and the negative light sensing signals S LS1− ˜S LSN− . The following describes operations of the distance calculation circuit  140  calculating the image distance R O1 . 
     As shown on the left of  FIG. 17 , during the distance sensing stage, the lighting/sensing control circuit  110  generates the light pulse signal S LD  representing “lit”, and the light source  102  emits the detection light ray L ID  to the touch point O 1 , such that the touch point O 1  generates the reflected light ray L RD . Then, the lighting/sensing control circuit  110  generates the shutter pulse signal S ST  representing “open”, such that the sensing units CS (Q,1) ˜CS (Q,N)  sense the energy of the reflected light ray L RD  and of the background light ray L B , and generate the light sensing signals S LS1 ˜S LSN , respectively. Then, the lighting/sensing control circuit  110  outputs the read signal S RE  representing “read”, such that the image sensor  101  outputs the light sensing signals S LS1 ˜S LSN  to the distance calculation circuit  140 , and the lighting/sensing control circuit  110  generates the phase signal S P  representing “sum” to indicate to the distance calculation circuit  140  that the received light sensing signals are in the distance sensing stage, i.e. the positive light sensing signals S LS1+ ˜S LSN+ . Set during the distance sensing stage, the reflected light ray L RD  mainly converges to form image on the sensing unit CS (Q,K) , and values of the positive light sensing signals S LS1+ ˜S LSN+  received by the distance calculation circuit  140  are as shown in the top-right of  FIG. 17 , the sensing unit CS (Q,K)  simultaneously senses the background light ray L B  and the reflected light ray L RD  (i.e. the touch point O 1  forms image on the sensing unit CS (Q,K) ). Therefore, the sensing signal S LSK+  equals the accumulated energy B K  of the sensing unit CS (Q,K)  sensing the background light ray L B  plus the accumulated energy R K  of the sensing unit CS (Q,K)  sensing the reflected light ray L RD , whereas other sensing units only receive the background light ray L B . Therefore, the sensing signal S LS1+  is equal to an accumulated energy B 1  of the sensing unit CS (Q,1)  sensing the background light ray L B ; the sensing signal S LS2+  is equal to an accumulated energy B 2  of the sensing unit CS (Q,2)  sensing the background light ray L B ; similarly, the sensing signal S LSN+  is equal to an accumulated energy B N  of the sensing unit CS (Q,N)  sensing the background light ray L B . 
     As shown on the left of  FIG. 17 , during the noise sensing stage, the lighting/sensing control circuit  110  generates the shutter pulse signal S ST  representing “open”, such that the sensing units CS (Q,1) ˜CS (Q,N)  sense the light rays converged by the lens LEN 1 , to generate the light sensing signals S LS1 ˜S LSN . However, the lighting/sensing control circuit  110  would then generate the light pulse signal S LD  representing “unlit”, and therefore the light source  102  does not emit the detection light ray L ID  to the touch point O 1 , nor does the touch point O 1  generate the reflected light ray L RD . Then the lighting/sensing control circuit  110  would output the read signal S RE  representing “read”, such that the image sensor  101  outputs the light sensing signals S LS1 ˜S LSN  to the distance calculation circuit  140 , and the lighting/sensing control circuit  110  generates the phase signal S P  representing “noise” to indicate to the distance calculation circuit  140  that the received light sensing signals are in the noise sensing stage, i.e. the negative light sensing signals S LS1− ˜S LSN− . Values of the light sensing signals S LS1− ˜S LSN−  received by the distance calculation circuit  140  are as shown in the bottom-right of  FIG. 17 . The shutter pulse signal S ST  has a same pulse width (duration T C ) during both the distance sensing stage and the noise sensing stage. Therefore, accumulated energy corresponding to the background light ray L B  of the light sensing signals S LS1 ˜S LSN  generated by the sensing units CS (Q,1) ˜CS (Q,N)  during the distance sensing stage and the noise sensing stage would be the same. In other words, the accumulated energy of the background light (B 1 ˜B N ) would be the same within the positive light sensing signals S LS1+ ˜S LSN+  as within the negative light sensing signals S LS1− ˜S LSN− . 
     After the distance sensing stage and the noise sensing stage, the lighting/sensing control circuit  110  generates the phase signal Sp representing “distance calculation”. The distance calculation circuit  140  would subtract the negative light sensing signals from the positive light sensing signals in the storage units, and select the storage units with maximum stored values after subtraction, to determine the position of the image formed by the reflected light ray L RD  on the image sensor  101  accordingly. In other words, values stored in the storage units M 1 ˜M N  of the distance calculation circuit  140  equal the values of the positive light sensing signals S LS1+ ˜S LSN+  subtracted by the values of the negative light sensing signals S LS1− ˜S LSN− , respectively. More specifically, the storage unit M 1  stores the positive light sensing signal S LS1−  and the negative light sensing signals S LS1− , and since both the positive light sensing signal S LS1+  and the negative light sensing signal S LS1−  equals B 1 , the value stored in the storage unit M 1  after subtraction would be zero; the storage unit M 2  stores the positive light sensing signal S LS2+  and the negative light sensing signals S LS2− , and since both the positive light sensing signal S LS2+  and the negative light sensing signal S LS2−  equals B 2 , the value stored in the storage unit M 2  after subtraction would be zero, and so forth. Similarly, the storage unit MK stores the positive light sensing signal S LSK+  and the negative light sensing signal S LSK− , and since the positive light sensing signal S LS2+  equals (B K +R K ) and the negative light sensing signals S LS2−  equals B K , the value stored in the storage unit M K  after subtraction would be R K ; the storage unit M N  stores the positive light sensing signal S LSN+  and the negative light sensing signals S LSN− , and since both the positive light sensing signal S LSN+  and the negative light sensing signal S LSN−  equals B N , the value stored in the storage unit M N  after subtraction would be zero. In other words, within the storage units M 1 -M N , the value of storage unit M K  equals R K , while values of all the other storage units equal zero; therefore, the distance calculation circuit  140  may select the storage unit M K  accordingly, i.e. the light sensing signal stored by the storage unit M K  has an energy corresponding to the reflected light ray L RD . Since the storage unit MK stores the light sensing signal generated by the sensing unit CS (Q,K) , the distance calculation circuit  140  may determine that the reflected light ray L RD  generated by the touch point O 1  mainly converges to form an image at the sensing unit CS (Q,K) . As such, the distance calculation circuit  140  may accordingly further derive an image position D CS  of the reflected light ray L RD  in  FIG. 16 , from the following equation:
 
 D   CS   =K×H   PIX   (1);
 
     Moreover, in  FIG. 16 , the line L F  formed between a focal point O F  of the lens LEN 1  and the sensing unit CS (Q,1)  is parallel to the detection light ray L ID ; therefore, an angle θ 1  formed by the detection light ray L ID  and the reflected light ray L RD  equals an angle θ 2  formed by the L F  and the reflected light ray L RD . In other words, a relationship between tan θ 1  and tan θ 2  may be expressed as follows:
 
tan θ 1   =L/D   M =tan θ 2   =D   CS   /D   F   (2);
 
     wherein L represents a predefined distance between the light source  102  and the image sensor  101  (the detection light ray L ID  and the line L F ), D CS  represents the image position of the reflected light ray L RD , D F  represents a focal distance of the lens LEN 1 . According to Eqn. (2), the image distance R O1  may be expressed as the following:
 
 R   O1 =( D   F   ×L )/ D   CS   (3);
 
     Therefore, the distance calculation circuit  140  may first calculate the image position D CS  via Eqn. (1), then calculate the image distance R O1  via Eqn. (3) according to the predefined distance L and the focal distance D F . 
     Simply put, in the distance measurement device  105 , the lighting/sensing control circuit  110  controls the light source  102  to emit the detection light ray L ID  to the touch point O 1  during the distance sensing stage, and the sensing units CS (Q,1) ˜CS (Q,N)  sense the light rays converged by the lens LEN 1  (e.g. the reflected light ray L RD  and the background light ray L B ), to generate the positive light sensing signals S LS1+ ˜S LSN+  accordingly, which are stored in the storage units M 1 ˜M N . During the noise sensing stage, the lighting/sensing control circuit  110  controls the light source  102  to not emit the detection light ray L ID , and the sensing units CS (2,1) ˜CS (Q,N)  sense the light rays converged by the lens LEN 1  (e.g. the reflected light ray L RD  and the background light ray L B ), to generate the negative light sensing signals S LS1 ˜S LSN−  accordingly, which are stored in the storage units M 1 ˜M N . At this point, values stored in the storage units M 1 ˜M N  would equal the positive light sensing signals S LS1+ ˜S LSN+  subtracted by the negative light sensing signals S LS1− ˜S LSN− . Therefore, the value of the storage unit M K  corresponding to the sensing unit CS (Q,K)  at which the reflected light ray L RD  converges would be higher than that of the other storage units. As such, the distance calculation circuit  140  may determine the sensing unit CS (Q,K)  at which the reflected light ray L RD  converges, and calculate the image position D CS  of the reflected light ray L RD  accordingly. Therefore, the distance calculation circuit  140  may calculate the image distance R O1  according to the image position D CS , the focal distance D F  of the lens LEN 1 , and the predefined distance L. 
     In summary, the optical touch display system of the present invention is capable of determining true coordinates for each of multiple touch points via verification by the distance measurement device. Therefore, the optical touch display system of the present invention may be utilized in multi-touch applications and can accurately determine the position of each touch point, providing the user with more convenient operation. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.