Patent Publication Number: US-9423893-B2

Title: Gesture detection device for detecting hovering and click

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan Patent Application Serial Number 102103850, filed on Jan. 31, 2013, the full disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field of the Disclosure 
     This disclosure generally relates to a human-machine interaction system and, more particularly, to an optical gesture detection device capable of performing the hover detection and the click detection. 
     2. Description of the Related Art 
     As the hand gesture control is operated according to human instinct such that it is widely applied to home appliances and portable electronic devices. The user can implement the specific function only by giving predetermined postures. In this way, more operating functions can be provided in addition to the traditional functions provided by pressing buttons. 
     The hand gesture control can be divided into the touch control and the hover control according to the operating method thereof, wherein the touch control system generally employs a touch panel such that the user can perform the slide control and the click control on the touch panel. However, the touch panel itself has a high manufacturing cost. 
     The hover control system generally utilizes an image sensor to detect the hovering gesture, i.e. the optical gesture control system. For example, a camera can be used to capture two-dimensional image frames and the move information can be identified according to the position variation of finger in the successive two-dimensional image frames. However, it is difficult for the hover control system to detect the click event, which is also an important issue in the field. 
     Accordingly, the present disclosure further provides a gesture detection device that may detect both the hovering operation and click operation by using at least two image sensors and eliminate the interference caused by ambient light. 
     SUMMARY 
     The present disclosure provides a gesture detection device that employs the linear image sensor array so as to reduce the cost and increase the number of detectable images per second. 
     The present disclosure further provides a gesture detection device that may eliminate the interference of ambient light by calculating the differential image thereby improving the identification accuracy. 
     The present disclosure provides a gesture detection device including a detection surface, a first image sensor, a second image sensor and a processing unit. The detection surface has a normal direction. The first image sensor is disposed on the detection surface and captures a first image along the normal direction. The second image sensor is disposed on the detection surface offsetting a predetermined distance from the first image sensor along a Z-axis and captures a second image along the normal direction. The processing unit is configured to calculate an X-axis coordinate according to a position of a pointer image in the first image or a pointer image in the second image, calculate a Y-axis coordinate according to a disparity of the pointer images in the first image and the second image, and identify a click event of the Z-axis when a size difference of the pointer images between the first image and the second image is larger than or equal to a difference threshold. 
     The present disclosure further provides a gesture detection device including a detection surface, a first image sensor, a second image sensor and a processing unit. The detection surface has a normal direction. The first image sensor is disposed on the detection surface and captures first images along the normal direction. The second image sensor is disposed on the detection surface parallel to the first image sensor and captures second images along the normal direction. The processing unit is configured to calculate an X-axis coordinate according to a position of a pointer image in the first images or a pointer image in the second images, calculate a Y-axis coordinate according to a disparity of the pointer images in the first images and the second images, and identify a click event when a size variation of the pointer images between the first images captured at different times and/or between the second images captured at different times is larger than or equal to a variation threshold. 
     The present disclosure further provides a gesture detection device including a detection surface, a first image sensor, a second image sensor, a third image sensor and a processing unit. The detection surface has a normal direction. The first image sensor is disposed on the detection surface and captures a first image along the normal direction. The second image sensor is disposed on the detection surface parallel to the first image sensor and captures a second image along the normal direction. The third image sensor is disposed on the detection surface offsetting a predetermined distance from the first image sensor and the second image sensor along a Z-axis and captures a third image along the normal direction. The processing unit is configured to calculate a two-dimensional coordinate according to the first image and the second image, and identify a click event of the Z-axis when a size difference between a pointer image in the first image and a pointer image in the third image or between a pointer image in the second image and the pointer image in the third image is larger than or equal to a difference threshold. 
     The present disclosure further provides a gesture detection device including a detection surface, a first image sensor, a second image sensor and a processing unit. The detection surface has a normal direction. The first image sensor is disposed on the detection surface and captures a first image along a direction deviating a predetermined angle from the normal direction. The second image sensor is disposed on the detection surface offsetting a predetermined distance from the first image sensor along a Z-axis and captures a second image along a direction deviating a negative predetermined angle from the normal direction. The processing unit is configured to calculate a two-dimensional coordinate according to positions of a pointer image in the first image and a pointer image in the second image, and identify a click event of the Z-axis when a size difference of the pointer images between the first image and the second image is larger than or equal to a difference threshold. 
     The present disclosure further provides a gesture detection device including a detection surface, a first image sensor, a second image sensor and a processing unit. The detection surface has a normal direction. The first image sensor is disposed on the detection surface and captures first images along a direction deviating a predetermined angle from the normal direction. The second image sensor is disposed on the detection surface parallel to the first image sensor and captures second images along a direction deviating a negative predetermined angle from the normal direction. The processing unit is configured to calculate a two-dimensional coordinate according to positions of a pointer image in the first images and a pointer image in the second images, and identify a click event when a size variation of the pointer images between the first images captured at different times and/or between the second images captured at different times is larger than or equal to a variation threshold. 
     The present disclosure further provides a gesture detection device including a detection surface, a first image sensor, a second image sensor, a third image sensor and a processing unit. The detection surface has a normal direction. The first image sensor is disposed on the detection surface and captures a first image along a direction deviating a predetermined angle from the normal direction. The second image sensor is disposed on the detection surface parallel to the first image sensor and captures a second image along a direction deviating a negative predetermined angle from the normal direction. The third image sensor is disposed on the detection surface offsetting a predetermined distance from the first image sensor and the second image sensor along a Z-axis and captures a third image along the normal direction. The processing unit is configured to calculate a two-dimensional coordinate according to the first image and the second image, and identify a click event of the Z-axis when a size difference between a pointer image in the first image and a pointer image in the third image or between a pointer image in the second image and the pointer image in the third image is larger than or equal to a difference threshold. 
     In one aspect, when sizes of the pointer images in the first image and the second image are substantially identical and larger than or equal to a predetermined size, it means that the pointer images are not finger images and thus the processing unit does not calculate the hover coordinate and does not identify the click event. 
     In one aspect, the gesture detection device may further include an infrared light source configured to illuminate field of views of the image sensors, wherein the infrared light source may emit light alternatively in a first brightness value and a second brightness value. The image sensors may respectively capture a bright image corresponding to the first brightness value and a dark image corresponding to the second brightness value. The processing unit may calculate a differential image between the bright image and the dark image captured by each image sensor so as to eliminate the interference of ambient light, wherein the first brightness value may be larger than the second brightness value, and the second brightness value may be zero or nonzero brightness. 
     In one aspect, the image sensors include a linear image sensor array, e.g. having 750 pixels in length and 1-6 pixels in width, to form a linear field of view. 
     The gesture detection device according to the embodiment of the present disclosure may be formed as an independent detection device and coupled to the electronic device having a screen, e.g. a smart TV, through wireless communication (for example, but not limited to, the bluetooth communication or microwave communication) or wired interface (for example, but not limited to, the USB interface). In addition, the gesture detection device according to the embodiment of the present disclosure may be directly integrated in the portable electronic device having a screen, e.g. notebook computers, personal digital assistances or cell phones. 
     In the gesture detection device according to the embodiment of the present disclosure, the image sensors may be arranged to capture image frames toward a direction substantially along a normal line or a direction inwardly deviating a predetermined angle from the normal line according to the distance between the image sensors such that a pointer image may simultaneously appear in field of views of all the image sensors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, advantages, and novel features of the present disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
         FIG. 1  shows a schematic block diagram of the gesture detection device according to an embodiment of the present disclosure. 
         FIGS. 2A and 2B  show schematic diagrams of the gesture detection device according to a first embodiment of the present disclosure. 
         FIGS. 3A and 3B  show schematic diagrams of the gesture detection device according to a second embodiment of the present disclosure. 
         FIGS. 4A-4C  show schematic diagrams of an electronic device in cooperation with the gesture detection device according to the embodiment of the present disclosure. 
         FIG. 5  shows an upper view of a first aspect of the gesture detection device according to the embodiment of the present disclosure. 
         FIG. 6  shows an upper view of a second aspect of the gesture detection device according to the embodiment of the present disclosure. 
         FIGS. 7A-7C  show upper views of a third aspect of the gesture detection device according to the embodiment of the present disclosure. 
         FIG. 8  shows a schematic diagram of calculating an X-axis coordinate in the gesture detection device according to the embodiment of the present disclosure. 
         FIG. 9  shows a schematic diagram of calculating a Y-axis coordinate in the gesture detection device according to the embodiment of the present disclosure. 
         FIGS. 10A and 10B  show schematic diagrams of identifying a click event in the gesture detection device according to the embodiment of the present disclosure. 
         FIG. 11  shows a schematic diagram of calculating the two-dimensional coordinate of a hovering pointer in the gesture detection device according to the embodiment of the present disclosure. 
         FIG. 12  shows a schematic diagram of the lighting of light source and the image capturing of image sensor in the gesture detection device according to the embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT 
     It should be noted that, wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     Referring to  FIG. 1 , it shows a schematic block diagram of the gesture detection device  1  according to an embodiment of the present disclosure. The gesture detection device  1  includes at least two image sensors, a processing unit  12  and a light source  13 . The number of the image sensors may be determined according to different applications. In one embodiment, the gesture detection device  1  may include a first image sensor (S 1 )  111  and a second image sensor (S 2 )  112 . In another embodiment, the gesture detection device  1  may include a first image sensor (S 1 )  111 , a second image sensor (S 2 )  112  and a third image sensor (S 3 )  113 . The processing unit  12  may be a digital signal processor and configured to receive image frames outputted by the at least two image sensors for post-processing to accordingly identify a two-dimensional coordinate of the hovering operation and a click event. The light source  13  is configured to illuminate field of views of the at least two image sensors and preferably emit invisible light, e.g. infrared light. In one embodiment, in order to eliminate the interference from ambient light, the light source  13  may emit light with different brightness values corresponding to the image capturing of the at least two image sensors (described later). 
     In addition, in order to decrease the cost and increase the number of detectable images per second, the at least two image sensors may be active image sensors, e.g. CMOS image sensors, and respectively may include a linear image sensor array, wherein the term “linear” herein is referred to the image sensor array having a length much larger than a width thereof, e.g. 750 pixels in length and 1-6 pixels in width so as to form a linear field of view. In addition, the light source  13  may be formed by arranging a plurality of active light sources or may be a single active light source (e.g. LED) as long as enough brightness can be provided thereby. 
     Referring to  FIGS. 2A and 2B , they show schematic diagrams of the gesture detection device  1  according to a first embodiment of the present disclosure, which includes a detection surface  10 , and a normal direction of the detection surface  10  is indicated by “n”. The first image sensor  111  and the second image sensor  112  are disposed on the detection surface  10  and configured to capture image frames substantially toward the normal direction “n”; that is, the first image sensor  111  and the second image sensor  112  are arranged in the way so that sensing surfaces thereof are substantially parallel to the detection surface  10 . In one embodiment, the first image sensor  111 , the second image sensor  112  and the light source  13  may be disposed at an inner side of the detection surface  10  as shown in  FIG. 2A . In another embodiment, the first image sensor  111 , the second image sensor  112  and the light source  13  may be disposed on the detection surface  10  as shown in  FIG. 2B . In this embodiment, center lines of the field of views of the first image sensor  111  and the second image sensor  112  may have an included angle, e.g. 0-20 degrees, with respect to the normal direction “n” so as to use the hovering operation algorithm of the first embodiment of the present disclosure mentioned below to calculate the hover coordinate, wherein the included angle preferably rotate toward a center position between the two image sensors. 
     Referring to  FIGS. 3A and 3B , they show schematic diagrams of the gesture detection device  1  according to a second embodiment of the present disclosure, which includes a detection surface  10 , and a normal direction of the detection surface  10  is indicated by “n”. The first image sensor  111  and the second image sensor  112  are disposed on the detection surface  10  and configured to capture image frames toward a direction deviating a predetermined angle from the normal direction “n”; that is, the first image sensor  111  and the second image sensor  112  are arranged in the way so that sensing surfaces thereof rotate with respect to the detection surface  10  by the predetermined angle. In one embodiment, the first image sensor  111 , the second image sensor  112  and the light source  13  may be disposed at an inner side of the detection surface  10  as shown in  FIG. 3A . In another embodiment, the first image sensor  111 , the second image sensor  112  and the light source  13  may be disposed on the detection surface  10  as shown in  FIG. 3B . In this embodiment, center lines of the field of views of the first image sensor  111  and the second image sensor  112  preferably have a predetermined angle, e.g. θ=30-60 degrees, with respect to the normal direction “n” so as to use the hovering operation algorithm of the second embodiment of the present disclosure mentioned below to calculate the hover coordinate, wherein the predetermined angle preferably rotate toward a center position between the two image sensors. As shown in  FIGS. 3A and 3B , the first image sensor  111  rotates an angle of +θ whereas the second image sensor  112  rotates an angle of −θ, wherein the symbols ± herein indicate opposite rotation directions. 
     It is appreciated that when the image sensors are disposed at an inner side of the detection surface  10 , preferably at least a part of the detection surface  10  is transparent to the light emitted by the light source  13 ; for example, a transparent cover may be used to cover thereon so as to protect elements inside the detection surface  10 . When the image sensors and the light source are disposed on the detection surface  10 , a transparent cover may also be used to cover thereon so as to protect the elements. 
     The gesture detection device  1  according to the embodiment of the present disclosure may be integrated with a portable electronic device, e.g. a notebook computer, a tablet computer, a cell phone or a personal digital assistance and configured to detect a hover coordinate of a pointer (e.g. a finger) and a click event as shown in  FIG. 4A . In addition, the gesture detection device  1  may be formed as an independent device and wired (as shown in  FIG. 4B ) or wirelessly (as shown in  FIG. 4C ) coupled to an electronic device  9  having a screen, e.g. a computer system, a television or a projection system. It is appreciated that the gesture detection device  1  may include a transmission unit configured to wired or wirelessly transmit the detected results to the electronic device  9 . In one embodiment, the hover coordinate detected by the gesture detection device  1  may be used to control the motion of a cursor  91 , and the click event (e.g. a single click or multi-click) may be used to activate an application associated with a selected icon. 
     Referring to  FIGS. 2A, 2B and 5 ,  FIG. 5  shows an upper view of a first aspect of the gesture detection device  1  according to the first embodiment of the present disclosure. In this aspect, the first image sensor  111  is disposed on the detection surface  10  and configured to capture a first image IF 1  substantially along the normal direction “n”; the second image sensor  112  is disposed on the detection surface  10  offsetting a predetermined distance D from the first image sensor  111  along a Z-axis and configured to capture a second image IF 2  substantially along the normal direction “n”; and the processing unit  12  is configured to calculate an X-axis coordinate according to a position of a pointer image in the first image IF 1  or the second image IF 2 , calculate a Y-axis coordinate according to a disparity of pointer images in the first image IF 1  and the second image IF 2 , and identify a click event along the Z-axis when a size difference of the pointer images between the first image IF 1  and the second image IF 2  is larger than or equal to a difference threshold. Methods of identifying the X-axis coordinate, the Y-axis coordinate and the click event are described below. 
     Referring to  FIG. 8 , when a pointer image Ip is contained in the first image IF 1  or the second image IF 2 , the pointer image Ip may cover a plurality of pixels. The processing unit  12  may calculate a position of the pointer image Ip (e.g. a center position or a gravity center position of the pointer image Ip) to be served as the X-axis coordinate. For example in one embodiment, it is assumed that the image sensor includes a linear image sensor array having a size of 750×1 such that every pixel position within an operable range 0-Rx (e.g. 0-750 herein) may be set to respectively correspond to one X-axis coordinate. Therefore, the processing unit  12  may calculate a position of the pointer image Ip within the operable range 0-Rx to be served as the X-axis coordinate. 
     If the X-axis coordinate is configured to be mapped to a projection screen, the processing unit  12  may further map the X-axis coordinate onto a correct position of the projection screen according to a ratio relationship between an X-axis resolution of the projection screen and the operable range, wherein the mapping method is well known and thus details thereof are not described herein. It is appreciated that in this embodiment, the operable range may include only the central part of the linear image sensor array (for example, but not limited to, from 50 pixels to 700 pixels) without including pixels at two edges so as to avoid miscalculation of the position when the pointer image Ip locates at the two edges. 
     Referring to  FIG. 9 , when the first image IF 1  and the second image IF 2  respectively contain a pointer image, the processing unit  12  respectively calculates a position (e.g. a center position or a gravity center position) of a first pointer image Ip 1  in the first image IF 1  and a second pointer image Ip 2  in the second image IF 2 . Then, the processing unit  12  calculates a position difference between positions of the first pointer image Ip 1  and the second pointer image Ip 2  to be served as a disparity. For example, when a pointer is farther from the image sensors, the first pointer image Ip 1  and the second pointer image Ip 2  are closer to each other; whereas when the pointer is closer to the image sensors, the first pointer image Ip 1 ′ and the second pointer image Ip 2 ′ are farther from each other. Therefore, every disparity may be set to correspond to one Y-axis coordinate, and the processing unit  12  may calculate the disparity to be served as the Y-axis coordinate. 
     It is appreciated that the gesture detection device  1  according to the embodiment of the present disclosure may include a storage unit configured to save the relation between the X-axis coordinate versus the position of the pointer image Ip and the relation between the Y-axis coordinate versus the disparity. 
     Referring to  FIG. 10A , in this aspect the first image sensor  111  and the second image sensor  112  are configured to detect a hovering operation of a finger and a click event. For example, at time t 1 , if the first pointer image Ip 1  in the first image IF 1  and the second pointer image Ip 2  in the second image IF 2  have substantially identical areas or widths, it means that it is the finger of user between the first image sensor  111  and the second image  112 , and the user is performing the hovering operation now. In hovering operation the X-axis coordinate and Y-axis coordinate may be calculated by the method of  FIGS. 8 and 9  to be served as the two-dimensional hover coordinate. At time t 2 , if the first pointer image Ip 1  in the first image IF 1  and the second pointer image Ip 2  in the second image IF 2  have different areas or widths, it means that the finger of user is moved forward (i.e. along the Z-axis) such that the first image sensor  111  detects the finger image but the second image sensor  12  detects a partial image of the fist or palm. In this case, it is able to identify that a click event occurs at the time t 2 . In this embodiment, when the processing unit  12  identifies that a size difference of the pointer images between the first image IF 1  and the second image IF 2  captured at the same time (i.e. the same sampling period) is larger than or equal to a difference threshold, a click event along the Z-axis is identified. 
     In addition, in this aspect the processing unit  12  identifies the size difference of the pointer images between the image frames captured at the same sampling period by different image sensors, and the purpose is to distinguish the difference between finger image from fist image or palm image. However, when the first image sensor  111  and the second image sensor  112  detect images of other parts of human body (e.g. a wrist image), the first pointer image Ip 1  in the first image IF 1  and the second pointer image Ip 2  in the second image IF 2  may also have substantially identical widths or areas. In order to avoid this situation, when sizes of the pointer images in the first image IF 1  and the second image IF 2  are larger than a predetermined size (e.g. an upper limit may be set according to actual finger images), the processing unit may not activate so as to avoid misoperation; that is, the X-axis coordinate and the Y-axis coordinate are not calculated and the click event is not identified. 
     In addition, in order to eliminate the interference from ambient light, the light source  13  may emit light with difference brightness values corresponding to the image capturing of the first image sensor  111  and the second image sensor  112 . For example referring to  FIG. 12 , the light source  13  emits light alternative in a first brightness value B 1  and a second brightness value B 2  corresponding to the image capturing of the image sensors. The first image sensor  111  and the second image sensor  112  respectively capture a bright image IF B  corresponding to the first brightness value B 1  and respectively capture a dark image IF D  corresponding to the second brightness value B 2 . The processing unit  12  further calculates a differential image (IF B −IF D ) between the bright image IF B  and the dark image IF D  captured by each image sensor so as to eliminate the interference from ambient light, wherein the second brightness value B 2  may be zero or nonzero brightness. In other words, in the above aspect, the first image IF 1  and the second image IF 2  may both be differential images. In this aspect, the bright image is referred to an image frame captured when the light source  13  turns on and the dark image is referred to an image frame captured when the light source  13  turns off or emits light in a lower brightness value. 
     Referring to  FIGS. 2A, 2B and 6 ,  FIG. 6  shows an upper view of a second aspect of the gesture detection device  1  according to the first embodiment of the present disclosure. In this aspect, the first image sensor  111  is disposed on the detection surface  10  and configured to capture first images IF 1  substantially along the normal direction “n”; the second image sensor  112  is disposed on the detection surface  10  parallel to the first image sensor  111  (i.e. no position offset along the Z-axis) and configured to capture second images IF 2  substantially along the normal direction “n”; and the processing unit  12  is configured to calculate an X-axis coordinate according to a position of a pointer image in the first images IF 1  or the second images IF 2 , calculate a Y-axis coordinate according to a disparity of pointer images in the first images IF 1  and the second images IF 2 , and identify a click event when a size variation of the pointer images between the first images IF 1  captured at different times and/or between the second images IF 2  captured at different times is larger than or equal to a variation threshold. The difference between the second aspect and the first aspect is that in the second aspect there is no position offset between the first image sensor  111  and the second image sensor along the Z-axis. In this aspect, methods of calculating the X-axis coordinate and the Y-axis coordinate are identical to those of the first aspect (referring to  FIGS. 8 and 9 ) and thus details thereof are not repeated herein. The method of identifying the click event is illustrated hereinafter. 
     Referring to  FIG. 10B , in this aspect the first image sensor  111  and the second image sensor  112  are also configured to detect a hovering operation of a finger and a click event. For example at time t 1 , if the first pointer image Ip 1  in the first image IF 1  and the second pointer image Ip 2  in the second image IF 2  have substantially identical areas or widths, it means that it is the finger of user between the first image sensor  111  and the second image  112 , and the user is performing the hovering operation now. In hovering operation the X-axis coordinate and Y-axis coordinate may be calculated by the method of  FIGS. 8 and 9  to be served as the two-dimensional hover coordinate. At time t 2 , if the areas or widths of the first pointer image Ip 1 ′ in the first image IF 1  and the second pointer image Ip 2  in the second image IF 2 ′ have a change, it means that the finger of user is moved forward such that the first image sensor  111  and/or the second image sensor  12  detects a partial image of the fist or palm, and it is able to identify that a click event occurs at the time t 2 . In this embodiment, when the processing unit  12  identifies a size variation (e.g. the size variation between Ip 1  and Ip 1 ′ and/or the size variation between Ip 2  and Ip 2 ′) of the pointer images between the first images IF 1  captured at different times (i.e. different sampling times, e.g. t 1  and t 2 ) and/or between the second images IF 2  captured at different times is larger than or equal to a variation threshold, a click event along the Z-axis is identified, wherein the size variation associated with the first images IF 1  and the second images IF 2  may be different. In this aspect, the times t 1  and t 2  are preferably two adjacent sampling times. 
     As mentioned above, in order to avoid misoperation, in this aspect when sizes of the pointer images in the first image IF 1  and the second image IF 2  are larger than a predetermined size, the processing unit  12  does not activate. 
     Similarly, in order to eliminate the influence of ambient light, in this aspect the light source  13  may emit light of different brightness values alternatively corresponding to the image capturing of the image sensors  111  and  112  as shown in  FIG. 12  to allow the processing unit  12  to calculate the differential image. 
     Referring to  FIGS. 2A, 2B and 7A ,  FIG. 7A  shows an upper view of a third aspect of the gesture detection device  1  according to the first embodiment of the present disclosure. This aspect includes a first image sensor  111 , a second image sensor  112  and a third image sensor  113 , wherein the first image sensor  111  is disposed on the detection surface  10  and configured to capture a first image IF 1  substantially along the normal direction “n”; the second image sensor  112  is disposed on the detection surface  10  parallel to the first image sensor  111  (i.e. no position offset along the Z-axis) and configured to capture a second image IF 2  substantially along the normal direction “n”; and the third image sensor  113  is disposed on the detection surface  10  offsetting a predetermined distance D from the first image sensor  111  and the second image sensor along a Z-axis and configured to capture a third image IF 3  substantially along the normal direction “n”. In this aspect, the processing unit  12  is configured to calculate a two-dimensional coordinate according to the first image IF 1  and the second image IF 2 ; i.e. the X-axis coordinate and Y-axis coordinate, wherein the method of calculating the two-dimensional coordinate is identical to that of the first aspect (referring to  FIGS. 8 and 9 ) and thus details thereof are not repeated herein. In addition, the processing unit  12  is further configured to identify a click event along the Z-axis when a size difference between a pointer image in the first image IF 1  and a pointer image in the third image IF 3  or between a pointer image in the second image IF 2  and the pointer image in the third image IF 3  is larger than or equal to a difference threshold, wherein the method of identifying a click event is identical to that of the first aspect (referring to  FIG. 10A ) and thus details thereof are not repeated herein. 
     More specifically speaking, in the third aspect the processing unit  12  calculates the two-dimensional coordinate according to the two image sensors disposed in parallel (similar to  FIG. 6 ) and identifies the click event according to the two image sensors having a position offset along the Z-axis (similar to  FIG. 5 ). However, the arrangement of the image sensors is not limited to  FIG. 7A , the image sensors may be arranged in the way as shown in  FIGS. 7B and 7C , wherein in  FIGS. 7A-7C  the hover coordinate is calculated according to the image frames captured by the first image sensor  111  and the second image sensor  112 . In addition in  FIG. 7B , the processing unit  12  identifies the click event according to the image frames captured by the second image sensor  112  and the third image sensor  113 . In  FIG. 7C , the processing unit  12  identifies the click event according to the image frames captured by the first image sensor  11  and the third image sensor  113 . 
     As mentioned above, in order to avoid misoperation, in this aspect when sizes of the pointer images in the first image IF 1  and the second image IF 2  are larger than a predetermined size, the processing unit  12  does not activate. 
     Similarly, in order to eliminate the influence of ambient light, in this aspect the light source  13  may emit light of different brightness values alternatively corresponding to the image capturing of the image sensors  111  to  113  as shown in  FIG. 12  to allow the processing unit  12  to calculate the differential image. 
     Referring to  FIGS. 3A, 3B and 5 ,  FIG. 5  shows an upper view of a first aspect of the gesture detection device  1  according to the second embodiment of the present disclosure. In this aspect, the first image sensor  111  is disposed on the detection surface  10  and configured to capture a first image IF 1  toward a direction deviating a predetermined angle (e.g. +θ) from the normal direction “n”; the second image sensor  112  is disposed on the detection surface  10  offsetting a predetermined distance D from the first image sensor  111  along a Z-axis and configured to capture a second image IF 2  toward a direction deviating a negative predetermined angle (e.g. −θ) from the normal direction “n”; and the processing unit  12  is configured to calculate a two-dimensional coordinate according to positions of pointer images in the first image IF 1  and the second image IF 2 , and identify a click event along the Z-axis when a size difference of the pointer images between the first image IF 1  and the second image IF 2  is larger than or equal to a difference threshold. The difference between this aspect and the first aspect of the first embodiment is that in this aspect the image sensors incline a predetermined angle (e.g. θ) toward each other to capture images such that the pointer may be within field of views of all image sensors when the image sensors are separated by a larger distance. In this aspect, the method of identifying the click event is identical to that of the first aspect of the first embodiment (referring to  FIG. 10A ); i.e. when the processing unit  12  identifies that a size difference (e.g. the difference between Ip 2 ′ and Ip 1 ′) of the pointer images between the first image IF 1  and the second image IF 2  captured at the same time is larger than or equal to a difference threshold, a click event along the Z-axis is identified. The method of calculating the two-dimensional coordinate is illustrated hereinafter. 
     Referring to  FIG. 11 , in this aspect the X-axis coordinate and the Y-axis coordinate may be obtained simultaneously according to the first image IF 1  and the second image IF 2 . For example, each position of the first image IF 1  and the second image IF 2  corresponds to a relative angle of the pointer position. Accordingly, when a pointer enters field of views of the first image sensor  111  and the second image sensor  112 , the processing unit  12  may calculate a pointer image position (e.g. the center or gravity center) of pointer images in the first image  111  and the second image  112 , and each pointer image position corresponds to one angle, e.g. 30 and 60 degrees shown herein. Meanwhile, if one of the first image sensor  111  and the second image sensor  112  is set as the original point, i.e. having a plane coordinate (0,0), two linear equations, e.g. L 1  and L 2  may be determined. The processing unit  12  may calculate the cross point coordinate of the two linear equations L 1  and L 2  to be served as the two-dimensional coordinate of the pointer position. In another embodiment, a lookup table of two-dimensional coordinates versus two angles associated with pointer image positions may be constructed previously, and the processing unit  12  may determine the two-dimensional coordinate according to the pointer image positions in the first image IF 1  and the second image IF 2  as well as the lookup table. 
     As mentioned above, in order to avoid misoperation, in this aspect when sizes of the pointer images in the first image IF 1  and the second image IF 2  are larger than a predetermined size, the processing unit  12  does not activate. 
     Similarly, in order to eliminate the influence of ambient light, in this aspect the light source  13  may emit light of different brightness values alternatively corresponding to the image capturing of the image sensors  111  and  112  as shown in  FIG. 12  to allow the processing unit  12  to calculate the differential image. 
     Referring to  FIGS. 3A, 3B and 6 ,  FIG. 6  shows an upper view of a second aspect of the gesture detection device  1  according to the second embodiment of the present disclosure. In this aspect, the first image sensor  111  is disposed on the detection surface  10  and configured to capture first images IF 1  toward a direction deviating a predetermined angle (e.g. +θ) from the normal direction “n”; the second image sensor  112  is disposed on the detection surface  10  parallel to the first image sensor  111  (i.e. no position offset along the Z-axis) and configured to capture second images IF 2  toward a direction deviating a negative predetermined angle (e.g. −θ) from the normal direction “n”; and the processing unit  12  is configured to calculate a two-dimensional coordinate according to positions of pointer images in the first images IF 1  and the second images IF 2 , and identify a click event when a size variation of the pointer images between the first images IF 1  captured at different times (i.e. different sampling times) and between the second images IF 2  captured at different times is larger than or equal to a variation threshold. The difference between this aspect and the second aspect of the first embodiment is that in this aspect the image sensors incline a predetermined angle (e.g. θ) toward each other to capture images such that the pointer may be within field of views of all image sensors when the image sensors are separated by a larger distance. In this aspect, the method of identifying the click event is identical to that of the second aspect of the first embodiment (referring to  FIG. 10B ); i.e. when the processing unit  12  identifies a size variation (e.g. the size variation between Ip 1  and Ip 1 ′ and/or the size variation between Ip 2  and Ip 2 ′) of the pointer images between the first images IF 1  captured at different times and/or between the second images IF 2  captured at different times is larger than or equal to a variation threshold, a click event along the Z-axis is identified. The method of calculating the two-dimensional coordinate is identical to that of the first aspect of the second embodiment (referring to  FIG. 11 ) and thus details thereof are not repeated herein. 
     Briefly speaking, the processing unit  12  identifies the click event according to the variation of the pointer images between the image frames captured at different sampling times by the image sensors, and determines the two-dimensional coordinate according to two linear equations formed according to positions of the pointer images in the first image IF 1  and the second image IF 2  or according to a lookup table and positions of the pointer images in the first image IF 1  and the second image IF 2 . 
     As mentioned above, in order to avoid misoperation, in this aspect when sizes of the pointer images in the first image IF 1  and the second image IF 2  are larger than a predetermined size, the processing unit  12  does not activate. 
     Similarly, in order to eliminate the influence of ambient light, in this aspect the light source  13  may emit light of different brightness values alternatively corresponding to the image capturing of the image sensors  111  and  112  as shown in  FIG. 12  to allow the processing unit  12  to calculate the differential image. 
     Referring to  FIGS. 3A, 3B and 7A ,  FIG. 7A  shows an upper view of a third aspect of the gesture detection device  1  according to the second embodiment of the present disclosure. This aspect includes a first image sensor  111 , a second image sensor  112  and a third image sensor  113 , wherein the first image sensor  111  is disposed on the detection surface  10  and configured to capture a first image IF 1  toward a direction deviating a predetermined angle (e.g. +θ) from the normal direction “n”; the second image sensor  112  is disposed on the detection surface  10  parallel to the first image sensor  111  (i.e. no position offset along the Z-axis) and configured to capture a second image IF 2  toward a direction deviating a negative predetermined angle (e.g. −θ) from the normal direction “n”; and the third image sensor  113  is disposed on the detection surface  10  offsetting a predetermined distance D from the first image sensor  111  and the second image sensor  112  along a Z-axis and configured to capture a third image IF 3  substantially along the normal direction “n”. In this aspect, the processing unit  12  is configured to calculate a two-dimensional coordinate according to the first image IF 1  and the second image IF 2 ; i.e. the X-axis coordinate and Y-axis coordinate, wherein the method of calculating the two-dimensional coordinate is identical to that of the first aspect of the second embodiment (referring to  FIG. 11 ) and thus details thereof are not repeated herein. In addition, the processing unit  12  is further configured to identify a click event along the Z-axis when a size difference between a pointer image in the first image IF 1  and a pointer image in the third image IF 3  or between a pointer image in the second image IF 2  and the pointer image in the third image IF 3  is larger than or equal to a difference threshold, wherein the method of identifying a click event is identical to that of the first aspect of the first embodiment (referring to  FIG. 10A ) and thus details thereof are not repeated herein. In addition, a deviation direction of the center line of the field of view of the third image sensor  113  with respect to the normal line may be determined according to the disposed position of the third image sensor  113 . For example, in  FIG. 7B  the third image sensor  113  may rotate toward the right hand side (e.g. +θ) whereas in  FIG. 7C  the third image sensor  113  may rotate toward the left hand side (e.g. −θ). 
     Briefly speaking, in this aspect the processing unit  12  identifies the click event according to the difference between pointer images in the image frames captured at the same sampling time by the two image sensors having a position offset in the Z-axis, and determines the two-dimensional coordinate according to two linear equations formed according to positions of the pointer images in the two image sensors disposed in parallel or according to a lookup table and positions of the pointer images in the two image sensors disposed in parallel. 
     As mentioned above, in order to avoid misoperation, in this aspect when sizes of the pointer images in the first image IF 1  and the second image IF 2  are larger than a predetermined size, the processing unit  12  does not activate. 
     Similarly, in order to eliminate the influence of ambient light, in this aspect the light source  13  may emit light of different brightness values alternatively corresponding to the image capturing of the image sensors  111  to  113  as shown in  FIG. 12  to allow the processing unit  12  to calculate the differential image. 
     In every aspect of the present disclosure, the at least two image sensors (e.g.  111 - 113 ) preferably capture image frames synchronously. It should be mentioned that the XYZ-axes shown in  FIGS. 5-7C  are only intended to illustrate but not to limit the present disclosure. 
     As mentioned above, it is difficult for the conventional optical gesture recognition system to identify the click event so that the applicable functions are limited. Therefore, the present disclosure further provides a gesture detection device ( FIGS. 1, 2A-2B and 3A-3B ) that may perform both the hovering operation and the click operation and eliminate the environmental interference by calculating the differential image. 
     Although the disclosure has been explained in relation to its preferred embodiment, it is not used to limit the disclosure. It is to be understood that many other possible modifications and variations can be made by those skilled in the art without departing from the spirit and scope of the disclosure as hereinafter claimed.