FIELD OF THE INVENTION 
       [0001]    The present invention relates to the use of mobile phones to control external devices. More particularly, the invention relates to the use of a mobile phone camera as part of a system that operates external devices. 
       BACKGROUND OF THE INVENTION 
       [0002]    Many devices are nowadays capable of connecting and exchanging data with mobile devices. As a result, it is now possible to integrate mobile devices as the controlling element of a system that operates such devices. 
         [0003]    So far, the art has failed to provide useful applications of mobile phones to display control systems. It is an object of the present invention to provide a system and method that exploits the functionality of mobile phones to provide efficient control means for external devices. 
       SUMMARY OF THE INVENTION 
       [0004]    A method for controlling a device, comprises: 
         [0000]    a) providing a mobile device comprising a camera;
 
b) positioning said mobile device such that said camera acquires the image of an operator&#39;s hands;
 
c) analyzing the movements of said operator&#39;s hands to derive a control command therefrom; and
 
d) transmitting said control command to a controlled device.
 
         [0005]    In one embodiment of the invention the mobile device is a mobile phone. In another embodiment of the invention the controlled device is integral to the mobile phone, and in a further embodiment of the invention the controlled device is separate from the mobile device. 
         [0006]    Different controlled devices can be used in conjunction with the invention, and in one embodiment of the invention the controlled device is a projector. 
         [0007]    Control commands can be transmitted from the mobile device to the external device via any suitable channel, e.g., via WiFi. 
         [0008]    In another aspect the invention encompasses a system comprising: 
         [0000]    A) a controlled device;
 
B) a mobile device comprising a camera;
 
C) circuitry for deriving control commands from movements captured by said camera and for transmitting them to the controlled device.
 
         [0009]    As explained above, the camera and the controlled device can be integral to a mobile device, or separate therefrom. 
         [0010]    The invention is further directed to a mobile phone comprising a camera, a projector and circuitry for deriving control commands from movements captured by said camera and for operating said projector therewith. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    In the drawings: 
           [0012]      FIG. 1  schematically illustrates a setup in which an integrated mobile phone projector is controlled according to one embodiment of the invention; 
           [0013]      FIG. 2  schematically illustrates a mobile phone setup where an integrated projector is controlled by user hand gestures; 
           [0014]      FIG. 3  schematically illustrates a possible photo album application in which a user controls the integrated projector to move the photos with gestures; 
           [0015]      FIG. 4  illustrates how users gestures are viewed in a phone camera preview under different illumination conditions; 
           [0016]      FIG. 5  is a graph showing a waveform caused by a hand gesture as it is calculated from incoming camera frames when they are analyzed in a one-dimensional space; 
           [0017]      FIG. 6  is a graph showing several consecutive frame waveforms caused by a hand gesture as calculated from incoming camera frames when they are analyzed in a one-dimensional space; 
           [0018]      FIG. 7  is a graph showing a center of mass location in the X and Y planes as a function of time and incoming camera frames; 
           [0019]      FIG. 8  is a graph showing a filtered (after local extremum extraction) center of mass location in the X and Y planes as a function of time and incoming camera frames; 
           [0020]      FIG. 9  is an example showing how the center of mass shift in the X and Y planes during the frames sequence is recognized as a gesture; and 
           [0021]      FIG. 10  illustrates the mechanism of background image subtraction used in one embodiment of the invention to enhance contrast in very low light conditions. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    As will be appreciated by the skilled person the invention is not limited to be used with any particular device. However, for the purpose of illustration, in the description to follow reference will be made to a projector at the device that is controlled by the mobile phone. 
         [0023]    Modern mobile phones can incorporate a built-in projector (referred to hereinafter as “phone projector”) and, therefore, in the example to follow reference will be made to such integrated phone projector. It is however understood by the skilled person, as will be further elaborated in the following description, that the invention is suitable for use also with non-integrated devices, such as when a projector is not integrated within the mobile phone. 
         [0024]    Referring now to  FIG. 1  a mobile phone  1  is shown, which is provided with an integrated phone projector  2  and an integrated phone camera  3 . In the figure the projector is directed against a wall  4 , onto which the image projected by the projector will be displayed. When operating according to the invention the mobile phone is positioned such that camera is directed toward the presenter, such that the movements of the presenter&#39;s hands takes place essentially in the A-A plane, i.e., above the mobile phone. In another embodiment of the invention the camera may be oriented differently so as to capture hand movements of the presenter, taken from the side of the mobile phone and not above it. As will be appreciated by the skilled person the actual positioned relationship of the mobile phone camera and the presenter&#39;s hands may vary according to the different setups. 
         [0025]    According to the invention the camera captures the movement of the presenter&#39;s hands, which are translated into instructions to the projector. For instance, swiping the hand from right to left may mean “next slide”, and from left to right may mean “previous slide”. 
         [0026]    An additional example is a movie player with virtual button controls. When a user wants to play a movie, he makes with his hands a gesture that is configured to be interpreted as a “Play” command. A camera pointed to the user captures the user&#39;s movements and an algorithm engine analyzes the frames captured by the camera. The algorithm engine detects that the user made a gesture that is recognized as pressing a “Play” button with his hand and retrieves the corresponding event to the movie player application. The movie player application then calls initiates the playing of a movie. 
         [0027]    As will be appreciated by the skilled person it is important to be able to capture and analyze images in poor light, particularly when operating a projector in relative darkness. This result is made possible by exploiting the capability of the mobile phone camera. The robust algorithm that performs gesture detection task well in poor lighting conditions does so by filtering background noise and detecting the user&#39;s hand (or other object held by the user) and its movement pattern/direction. The detection is based on analyzing the one-dimensional signal pattern which is the integrated two-dimensional images in the direction orthogonal to the movement direction. The analysis of signal peaks will retain the gesture detection. 
         [0028]    In order to recognize hand gestures in low light, in one embodiment of the invention the following procedure is followed:
       1) The user moves his hand in front of the phone camera;   2) The camera captures the frames including the user&#39;s hand;   3) The captured frame is passed on to the gesture recognition core engine;   4) The minimum requirement for recognition is two sequential frames that contain a user&#39;s hand in them in order to determine the direction of movement;   5) The history of N past frames is stored;   6) When a new frame arrives, it is analyzed and statistics are calculated, such as: average intensity values in each row and columns, and a center of mass of the frame by intensity;   7) The difference in the integral intensity values between two sequential frames is calculated. This calculation is parallel to subtracting the unchanging background;   8) The resulting signal of row and column intensity sum difference is calculated to find a significant peak location;   9) The peak should exceed an adaptive threshold on intensity, which is correlated to the illumination intensity;   10) A correspondence is sought in the direction of peak propagation and the size of the peaks in consecutive frames;   11) Calculate center of mass shift between frames   12) Filter center of mass according to threshold and find local minimum   13) Combine center of mass shift data from X and Y dimensions to detect gesture   14) For detection with center of mass image blocks (2×2, 4×4) are tested independently   15) Detect gesture starting and end point to reduce misdetections   16) If all the conditions are met, the gesture is recognized and reported.       
 
         [0045]    Detection of the gesture in Z axis (vertical)
       17) Subtract background from the incoming frame   18) Calculate difference from background frame   19) Use dynamic threshold to detect center of mass shift       
 
         [0049]    Detection Criteria: 
         [0000]      | Sn−A|&gt;D*Env Th  1
 
         [0000]        |Sn |&gt;BaseTh  2
 
         [0000]        Sn−Sn− 1 &gt;S th (For moving heads cancellation)  3
 
         [0050]    Where,
       Sn: CoM shift for Frame n   A: CoM shift average   D: Standart deviation of CoM shift   EnvTh: numeric threshold that depends on average frame intensity   BaseTh: constant threshold (different for in gesture frames and out of gesture frames)   Sth: constant threshold for first derivation of the shift       
 
         [0057]    Direction Estimation:
       1) Compute center of mass global shifts   2) Analyze sign changes in center of mass during gesture to determine what gesture was performed.   3) If there was sign change or the sign hasn&#39;t changed but the center of mass shift is above threshold it is Up/Down/Right or Left.   4) Else it is a gesture in Z dimension       
 
         [0062]    Features for gesture separation:
       1) Center of mass shift sign   2) Total quadratic center of mass shift   3) Center of mass shift direction   4) Gesture duration   5) Number of similar frames   6) Contrast       
 
         [0069]    As will be appreciated by the skilled person the invention permits to control other equipment, such as for instance a standalone projector or a computer, as long as connectivity is established between the mobile phone and such equipment. For instance, connection between the cellular phone and equipment can be performed over WiFi, in which case the mobile phone operates as in the above example by “reading” the hand movements of the presenter, but then transmits appropriate commands to the external equipment over WiFi, instead of internally to a built-in device. 
         [0070]    The above examples and description have been provided for the purpose of illustration and are not intended to limit the invention in any way. Many different types of mobile devices (e.g., PDAs) provided with the camera can be used, in conjunction with any suitable built-in or external device, without exceeding the scope of the invention.
A method for controlling a device comprises: a) providing a mobile device comprising a camera; b) positioning said mobile device such that said camera acquires the image of an operator's hands; c) analyzing the movements of said operator's hands to derive a control command therefrom; and d) transmitting said control command to a controlled device.