Abstract:
A system for synchronizing the exposure of an image by a master camera with the exposure of an image by one or more slave cameras, each of which is located at a different position relative to a common subject to be photographed. Exposure synchronization is accomplished via an optical sensing system on each slave camera that detects a light pulse (e.g., a flash or strobe) from the master camera emitted simultaneously with the initiation of the exposure of the subject, causing the slave camera to trigger an exposure of the subject, if the detected light pulse is within the parameters of the image capture mode manually selected for a given camera. An image may thus be captured from each of the different angles, relative to the subject being photographed, at which the cameras are positioned.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to cameras and photography systems, and more particularly, to a system for photographing an event simultaneously using multiple cameras.  
         BACKGROUND OF THE INVENTION  
         [0002]    Statement of the Problem  
           [0003]    It is a problem to photograph a single event from multiple angles simultaneously using a plurality of cameras. Previously, an event could be photographed by a single camera using multiple slave flash triggers, each of which is connected to a separate flash unit. However, there was, heretofore, no simple method for synchronizing a plurality of cameras to essentially simultaneously photograph a single event from multiple perspectives, angles, or locations.  
           [0004]    Solution to the Problem  
           [0005]    The present system solves the above problem and achieves an advance in the field by synchronizing the capture of an image of a target subject by a master camera with the capture of an image of the subject by one or more slave cameras, each of which is located at a different position relative to the subject to be photographed.  
           [0006]    Initially, a light pulse is transmitted by a ‘master’ camera when the camera&#39;s shutter button is pressed. Image capture (exposure) synchronization of the slave cameras is accomplished via an optical sensing system on each slave camera that detects a light pulse (e.g., a flash or strobe) transmitted from the master camera which causes the slave camera&#39;s electronic ‘shutter’ to trigger and record an image present on the camera&#39;s CCD (the ‘charge-coupled device’ that detects the image) if the detected light pulse is within certain parameters. These parameters may be manually selected for each camera to establish an appropriate image capture mode for a particular situation. An image may thus be captured from each of the different angles, relative to the subject being photographed, at which the cameras are positioned.  
           [0007]    Any one of several image capture modes may be selected by a user of the present system. These modes include the detection of light pulses in the infrared, ultraviolet, and visible spectrum, as well as light pulses having a predetermined strobe pulse sequence or other characteristics. Slave cameras may also be triggered by light pulses emitted from other cameras (such as conventional film cameras) or flash units that emit any basic type of flash or strobe.  
           [0008]    The slave mode camera system disclosed herein is useful for capturing sporting events as well as social events such as birthday parties, weddings, and the like. The system may also be used for security monitoring and photographic recording of any event of potential interest, where it is advantageous to capture the event from multiple camera angles. In addition, the use of multiple camera angles can provide useful information in applications such as failure analysis of structures and in other types of testing environments.  
           [0009]    The present system also takes advantage of technology available in many existing digital cameras, requiring only the addition of software or firmware that functions in accordance with the method described herein. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1A illustrates components of interest in a digital camera programmed in accordance with the present system;  
         [0011]    [0011]FIG. 1B illustrates, in further detail, certain aspects of processor  110 ;  
         [0012]    [0012]FIG. 2 is a diagram showing an exemplary arrangement of a master camera and two slave cameras;  
         [0013]    [0013]FIG. 3 is a flowchart illustrating an exemplary set of steps performed by a slave camera in effecting the present system;  
         [0014]    [0014]FIG. 4 is a flowchart illustrating an exemplary set of steps performed by a master camera; and  
         [0015]    [0015]FIG. 5 is a diagram showing the timing relationships between strobes and image capture in a multiple camera scenario.  
     
    
     DETAILED DESCRIPTION  
       [0016]    [0016]FIG. 1A illustrates components of interest in a digital camera  101  programmed in accordance with the present system. As shown in FIG. 1, camera  101  comprises one or more light receiving devices including light sensor  105 , infrared serial port transceiver  106 , and CCD  107 , which is the charge-coupled device that detects the image to be photographed. Camera  101  further comprises one or more light transmitting devices including light emitter  104  and infrared serial port transceiver  106 . Each of the light receiving devices  105 / 106 / 107  and each of the light transmitting devices  104 / 106  is coupled to processor  110 . Processor  110  is also coupled to shutter button  103  and image capture mode switch  102 , the function of which is described in detail below. Although three light receiving devices  105 / 106 / 107  and two light transmitting devices  104 / 106  are shown in FIG. 1, the present system is operable with any one of the light receiving devices and any one of the light receiving devices shown therein. Note that the term ‘exposure’ is used herein to denote the process of image capture by a digital camera, notwithstanding the fact that a digital camera does not use photographic film.  
         [0017]    [0017]FIG. 1B illustrates, in further detail, certain aspects of an exemplary processor  110 . As shown in FIG. 1B, processor  110  provides a mode control function  111 ( 1 ) and a timer  114 . I/O interface block  120  in FIG. 1B includes a light input filter/decoder  112  and light output device driver  113 . Block  120  is shown in dotted lines as the I/O interface may be physically integrated with processor  110 , or functions provided by the interface may be performed by the processor in lieu of separate hardware devices. The functions provided by mode control unit  111 ( 1 ), filter/decoder  112 , driver  113 , and timer  114  (as explained below) may be optionally implemented by software, firmware, or hardware. In any event, the functions performed by blocks  110  and  120  are initiated in response to commands from processor  110 . Light receiving devices  105 / 106 / 107  are represented generically by light input (or optical input) device  108 , since only one of the devices  105 / 106 / 107  is required for operation of the present system. Light emitting devices  104  and  106  are likewise represented generically by light output device  109 , as only one of the devices  104 / 106  is required for system operation.  
         [0018]    In an exemplary embodiment of the present system, light output device  109  is a typical camera strobe light, and light input device  108  is the camera&#39;s CCD  107 , since this device detects the wavelength of light emitted by a typical camera strobe. In an alternative embodiment, light input device  108  may be an infrared light sensor  105  which responds to infrared light emitted by an infrared light output device  104  such as an IR transistor, an IR diode, an IRDA module, or the like.  
         [0019]    The present system typically operates with a normal camera flash unit (strobe light) functioning as light emitter  104 . The type of strobe (light pulse) emitted by a normal flash unit typically has a pulse duration between approximately 250 microseconds and  4  milliseconds, and comprises light in the visible spectrum between approximately 450 and 700 nanometers. In an alternative embodiment, the strobe may emit light in the infrared or ultraviolet spectral region. The present system may be programmed via image capture mode switch (or other input device)  102  for operation with many possible strobe types, as well as programmed to ignore potentially false trigger pulses such as pre-flashes used for red-eye reduction and exposure testing. In addition, a slave camera  101  may be set to a mode wherein it triggers the capture of an image (i.e., an exposure) only in response to receiving a light pulse from another camera having a specific strobe characteristic such as a predefined strobe pulse sequence and/or a specific wavelength. Other types of strobes  104  might include infrared (IR), and ultraviolet (UV) for specialized photography.  
         [0020]    [0020]FIG. 2 is a diagram showing an exemplary arrangement of a master camera and two slave cameras in accordance with the present system. As shown in FIG. 2, master camera  101 ( 1 ) and one or more slave cameras  101 ( 2 ) and  101 ( 3 ) are positioned so that all of the cameras are pointed at a target subject  201 . Each of the cameras is positioned at a different location to provide a corresponding different viewing angle of the target subject  201 .  
         [0021]    [0021]FIG. 5 is a diagram showing the timing relationships between strobes and image capture in a multiple camera scenario. Operation of the present system is best understood by viewing FIG. 2 and FIG. 5 in conjunction with one another.  
         [0022]    In operation, when shutter button  103  on master camera  101 ( 1 ) is pressed (at reference number/mark  500  in FIG. 5), the camera  101 ( 1 ) starts the exposure (image capture) Exp.  1  of the target subject  201 , and the camera&#39;s light output device  109  emits a light pulse  205  (FIG. 2) which is detected (at mark  501 ) by a light input device  108  on each slave camera  101 ( 2 ) and  101 ( 3 ). Slave camera  101 ( 2 ) then starts a timer  114  with a delay t 1  (Delay  1 ) sufficient to avoid ‘seeing’ the light pulse (strobe)  205  from master camera, e.g., 10 milliseconds. Delay t 1  is at least equal to, or preferably, slightly greater than (by approximately 15 to 25 percent) the length of time it takes for a typical light pulse  205  to decay to a level of zero or near-zero luminosity where it will not adversely affect the exposure of the slave camera. When the timer has expired (at mark  502 ), slave camera  101 ( 2 ) triggers its strobe  206  and starts the exposure Exp.  2  of the target subject  201 . When light pulse  205  is detected (at mark  501 ) by slave camera  101 ( 3 ), it starts a timer  114  with a delay equal to t 1 +t 1 (2×t 1 ), since this camera  101 ( 3 ) must wait until the light pulse  206  from the strobe of slave camera  101 ( 2 ) has decayed. In the general case, the nth slave camera in a given system will have a timer delay of n×t, where t is a value slightly greater than the duration of the light pulse being employed.  
         [0023]    Slave camera  101 ( 3 ) ignores strobe  206  from camera  101 ( 2 ), and at mark  503 , the timer for slave camera  101 ( 3 ) expires, and camera  101 ( 3 ) then triggers its strobe  207  and starts the exposure (Exp.  3 ) of the target subject  201 . An image of target subject  201  is thus captured in near simultaneity from each of the different angles, relative to the subject, at which the cameras  101 ( 1 )- 101 ( 3 ) are positioned.  
         [0024]    [0024]FIG. 3 is a flowchart illustrating an exemplary set of steps performed by a slave camera in carrying out a method in accordance with the present system. As shown in FIG. 3, at step  305 , a user sets the image capture mode for master camera  101 ( 1 ) using mode switch  102 . At step  305 , the image capture mode setting is input to mode control software or firmware to establish a number of manually selected parameters for a given camera for a particular situation. Any one, or a combination of these parameters may be selected to cause a camera  101  to initiate an exposure only when a received light pulse has characteristics that correspond with each of the parameters associated with a selected image capture mode. These parameters include:  
         [0025]    (a) the master or slave status of the camera;  
         [0026]    (b) for slave cameras, the slave&#39;s ‘firing’ order, i.e., whether this particular slave is the second, third, etc., camera to trigger a strobe/exposure;  
         [0027]    (c) the light output device  108  to be triggered;  
         [0028]    (d) the light input device  109  (if camera is a slave, or in the case of a master camera, where the camera is to be triggered remotely)  
         [0029]    (e) the strobe pulse coding sequence (if a predefined strobe pulse sequence is one of the parameters for a specific mode);  
         [0030]    (f) a specific wavelength range (if light pulses having a particular type of spectral characteristic are to be ignored); and  
         [0031]    (g) whether image capture by a camera in master camera mode is to be triggered by shutter button  103  or by an external strobe.  
         [0032]    The above parameters are pre-established in mode control unit  111 ( 1 ) via software, firmware, or hardware, prior to use of camera  101 . The image capture mode settings selected at a given time on each camera in the present system must correspond to one another; i.e., a corresponding slave camera must have a light input device  108  that is capable of detecting the wavelength and coding sequence, if any, of the strobe emitted by the master camera.  
         [0033]    For a given image capture mode, light output driver  113  may be used to implement a predefined strobe pulse coding sequence for a master or slave camera, and also to select the appropriate light output device. Filter/decoder  112  may be used, correspondingly, to detect a predefined strobe pulse coding sequence for a slave camera. IRDA serial port transceiver  106  may be used to facilitate the light pulse coding and communication between a master camera and one or more slave cameras. Filter/decoder  112  may also be used to signal processor  110  that an appropriate strobe has been detected by filtering out a predetermined range of wavelengths in accordance with a particular image capture mode to avoid unwanted triggering of a camera due to receiving strobes or light pulses from extraneous sources.  
         [0034]    Mode (f), above, may be implemented whereby a slave camera fires when any other basic type of strobe is detected. Therefore, a conventional film camera with a typical flash unit can be employed as a master camera in the present system.  
         [0035]    At step  310 , a user sets the image capture mode for a slave camera ( 101 ( 2 ), for example) using mode switch  102 . The image capture mode setting is then input to mode control software or firmware  111 ( 1 ) to establish the appropriate parameters, for the selected mode, for timer  114 , filter/decoder  112 , and light output driver  113 . At step  315 , master camera  101 ( 1 ) starts the exposure and triggers the light pulse in accordance with the selected mode.  
         [0036]    All remaining steps in FIG. 3 are performed by each of the slave cameras. At step  320 , the slave camera firmware  111  monitors the input from light input device  108 , as filtered and decoded by filter/decoder  112  (if filtering and/or decoding is necessary in accordance with the selected mode parameters). At step  325 , a light pulse reaches the camera, and at step  330 , firmware  111  determines whether the received pulse is within the parameters established for the selected mode, assuming that filter/decoder  112  has sent a signal, indicative of the type of light pulse, to firmware  111  in processor  110 . If no such signal is generated by filter/decoder  112 , or if firmware  111  determines that the signal received from filter  112  does not fall within the present image capture mode parameters, then the received light pulse is ignored, at step  335 , and monitoring continues at step  320 .  
         [0037]    At step  340 , delay timer  114  is started, as described above with respect to FIG. 5. Finally, at step  350 , when timer  114  times out, an exposure and a strobe are initiated by the slave camera.  
         [0038]    [0038]FIG. 4 is a flowchart illustrating an exemplary set of steps performed by a master camera  110 ( 1 ). As shown in FIG. 4, at step  405 , the image capture mode is selected by a user. At step  410 , the mode setting is then input to mode control software or firmware  111 ( 1 ) to establish the appropriate parameters, for the selected mode, for filter/decoder  112  and light output driver  113 . At step  415 , if the selected mode indicates that an exposure is to be triggered by an external strobe instead of shutter button  103 , then firmware  111  waits either for the strobe to be received at step  420 , or for the shutter button to be pressed at step  425 . Upon the detection of either the shutter button being pressed, or receipt of an external strobe (according to the selected mode), at step  430 , an exposure is initiated and the selected type of strobe is triggered via light output device driver  113  and the appropriate light output device  109 .  
         [0039]    It should be noted that the present system is operational with any number of slave cameras, and furthermore, that there is not necessarily any functional distinction between a camera used as a master camera and a camera used as a slave camera, other than the image capture mode in which a given camera may be operating at a specific time.  
         [0040]    While exemplary embodiments of the present invention have been shown in the drawings and described above, it will be apparent to one skilled in the art that various embodiments of the present invention are possible. For example, the specific sequence of steps described above in FIGS. 3 and 4, as well as the particular configuration of components shown in FIGS. 1A and 1B, should not be construed as limited to the specific embodiments described herein. Modification may be made to these and other specific elements of the invention without departing from its spirit and scope as expressed in the following claims.