Abstract:
A digital camera and method is provided that measures an ambient illumination in response to the shutter signal, performs preliminary light emission when the measured ambient illumination is less than a first reference value, delays main light emission by a predetermined time after the preliminary light emission, performs the main light emission after the predetermined time has lapsed, acquires image data during the main light emission, and processes the acquired image data.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This application claims the priority of Korean Patent Application No. 2003-44856, filed on Jul. 3, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
         [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a digital camera including a strobe unit and a method for controlling such a digital camera.  
         [0004]     2. Description of the Related Art  
         [0005]     A conventional strobe unit of a digital camera, for example, a flash light emitting device disclosed in U.S. Pat. No. 6,476,564, does not perform preliminary light emission that would allow a user to adjust image composition in a low-light environment. Because it is difficult for the user to adjust the composition of a subject to be photographed in a low-light environment, the user has difficulties in photographing images.  
         [0006]     To overcome this problem, a portable terminal such as a mobile phone including a digital camera may be equipped with an auxiliary lamp such as a light. emitting diode. However, such an auxiliary lamp has a much lower light intensity than a strobe lamp and thus is not helpful in remote photographing in a low-light environment. Moreover, a user needs to manually operate the auxiliary lamp according to his/her determination of the intensity of ambient illumination. Such manual operation is inconvenient and may incur unnecessary operation of the auxiliary lamp.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention provides a digital camera and method for emitting light adaptively so that a user can adjust photographic image composition in a low-light environment without needing to perform a special operation.  
         [0008]     According to an aspect of the present invention, a digital camera generates a shutter signal when a user presses a shutter button switch. The camera measures an ambient illumination in response to the shutter signal, performing preliminary light emission when the measured ambient illumination is less than a first reference value, delaying main light emission by a predetermined time after the preliminary light emission, performing the main light emission after the predetermined time has lapsed, and acquiring image data during the main light emission and processing the acquired image data.  
         [0009]     According to an aspect of the present invention, a method of controlling a digital camera comprises generating a shutter signal when a user presses a shutter button switch. The method comprises measuring an ambient illumination in response to the shutter signal, performing preliminary light emission when the measured ambient illumination is less than a first reference value, delaying main light emission by a predetermined time after the preliminary light emission, performing the main light emission after the predetermined time has lapsed, and acquiring image data during the main light emission and processing the acquired image data.  
         [0010]     In the present invention, the preliminary light emission is performed when the ambient illumination measured in response to the shutter signal is less than the first reference value, and then the main light emission is delayed by the predetermined time. Accordingly, under an ambient illumination less than the first reference value, a user can satisfactorily adjust photographic image composition without special operations before the main light emission and the image data acquisition are performed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The above and other features and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:  
         [0012]      FIG. 1  is a diagram of a digital camera according to the present invention;  
         [0013]      FIG. 2  is a flowchart of a photographic mode program performed by a central processing device show in  FIG. 1 , according to a first embodiment of the present invention;  
         [0014]      FIG. 3  is a flowchart of a photographic mode program performed by the central processing device show in  FIG. 1 , according to a second embodiment of the present invention; and  
         [0015]      FIG. 4  is a flowchart of a photographic mode program performed by the central processing device show in  FIG. 1 , according to a third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     Referring to  FIG. 1 , a digital camera of the present invention is installed in a portable terminal such as a mobile phone. The digital camera includes a central processing device  1 , a photographic unit  2 , a communication interface  3 , a function selection switch unit  4 , a strobe driver  5 , an audio output unit  6 , a display unit  7 , a power switch PS, a shutter button switch SS, a capacitor MC, and a strobe lamp XE.  
         [0017]     When a user turns the power switch PS on, the central processing device  1  performs a control algorithm according to an embodiment of the present invention, controls operations of each element, and transmits image data acquired by the photographic unit  2  to external devices via the communication interface  3 .  
         [0018]     The photographic unit  2  acquires image data and includes lenses, a photoelectric conversion element, and a digital-to-analog converter. The function selection switch unit  4  is manipulated by the user to select an operation of the central processing device  1 .  
         [0019]     When a user presses the shutter button switch SS, a shutter signal is generated and is input to the central processing device  1 . Control operations performed by the central processing device  1  in connection with the shutter signal will be described in detail later with reference to  FIGS. 2 through 4 . The strobe driver  5  charges the capacitor MC and drives the strobe lamp XE, for example, a xenon lamp, according to the control of the central processing device  1 .  
         [0020]     The audio output unit  6  processes a digital audio signal received via the central processing device  1  and outputs sound. The display unit  7  processes a digital display signal received via the central processing device  1  and displays the digital display signal.  
         [0021]     Hereinafter, a photographic mode program performed by the central processing device  1  according to a first embodiment of the present invention will be described with reference to  FIGS. 1 and 2 .  
         [0022]     The central processing device  1  initializes itself and other elements involved in photographic operations in step S 201 . When the current operation mode is determined to be a photographic mode in step S 202  and when a shutter signal is received from the shutter button switches SS in step S 203 , ambient illumination is measured in step S 204 .  
         [0023]     Next, when the measured ambient illumination is greater than or equal to a first reference value, for example, “3”, in step S 205 , preliminary light emission and main light emission are not performed. Subsequently, when the shutter signal is received from the shutter button switch SS in step S 206 , image data is acquired and processed by the photographic unit  2  in step S 214 . Next, the photographic mode program returns to step S 202 , allowing repetitive operation.  
         [0024]     However, when the measured ambient illumination is less than the first reference value in step S 205 , the following steps are performed.  
         [0025]     When the capacitor MC has not been completely charged in step S 207 , the capacitor MC is charged by the strobe driver  5  in step S 208 . Next, the strobe lamp XE is turned on by the strobe driver  5 , thereby performing preliminary light emission in step S 209 . Next, a 3-second timer is started in step S 210 . Thereafter, if the shutter signal is not received from the shutter button switch SS in step S 212  but a timer end signal is received in step S 211 , the photographic mode program returns to step S 203  because the user has not completely adjusted image composition. Meanwhile, after the 3-second timer is started, if the shutter signal is received from the shutter button switch SS in step S 212 , the strobe lamp XE is turned on by the strobe driver  5 , thereby performing main light emission in step S 213 , because the user has completed the adjustment of image composition. Next, image data is acquired by the photographic unit  2  in response to the main light emission in step S 214 . Thus, under low illumination, the user can satisfactorily adjust photographic image composition without special operations before the main light emission and image data acquisition are performed in steps S 213  and S 214 . Next, the photographic mode program returns to step S 202 , allowing repetitive operation.  
         [0026]     Hereinafter, a photographic mode program performed by the central processing device  1  according to a second embodiment of the present invention will be described with reference to  FIGS. 1 and 3 .  
         [0027]     The central processing device  1  initializes itself and other elements involved in photographic operations in step S 301 . When the current operation mode is determined to be a photographic mode in step S 302  and when a shutter signal is received from the shutter button switches SS in step S 303 , ambient illumination is measured in step S 304 .  
         [0028]     Next, when the measured ambient illumination is greater than or equal to a second reference value, for example, “9”, in steps S 305   a  and S 305   b , preliminary light emission and main light emission are not performed. Subsequently, when the shutter signal is received from the shutter button switch SS in step S 306 , image data is acquired and processed by the photographic unit  2  in step S 314 . Next, the photographic mode program returns to step S 302 , allowing repetitive operation.  
         [0029]     However, when the measured ambient illumination is less than the second reference value and greater than or equal to a first reference value, for example, “3”, in steps S 305   a  and S 3051   b , only the main light emission without the preliminary light emission is performed because the measured ambient illumination is sufficient for a user to adjust image composition although the main light emission is still required to obtain an image file. Thus, when the capacitor MC has not been completely charged in step S 307   b , the capacitor MC is charged by the strobe driver  5  in step S 308   b . Next, if the shutter signal is received from the shutter button switch in step S 315 , the strobe lamp XE is turned on by the strobe driver  5 , thereby performing the main light emission in step S 313 . Next, image data is acquired by the photographic unit  2  in response to the main light emission in step S 314 . Next, the photographic mode program returns to step S 302  for the repetitive operation.  
         [0030]     However, when the measured ambient illumination is less than the first reference value in step S 305   a , the following steps are performed.  
         [0031]     When the capacitor MC has not been completely charged in step S 307   a , the capacitor MC is charged by the strobe driver  5  in step S 308   a . Next, the strobe lamp XE is turned on by the strobe driver  5 , thereby performing the preliminary light emission in step S 309 . Next, a 3-second timer is started in step S 310 . Thereafter, if the shutter signal is not received from the shutter button switch SS in step S 312  but a timer end signal is received in step S 311 , the photographic mode program returns to step S 303  because the user has not completely adjusted image composition. Meanwhile, after the 3-second timer is started, if the shutter signal is received from the shutter button switch SS in step S 312 , the strobe lamp XE is turned on by the strobe driver  5 , thereby performing the main light emission in step S 313 , because the user has completed the adjustment of image composition. Next, image data is acquired by the photographic unit  2  in response to the main light emission in step S 314 . Accordingly, under a low illumination, the user can satisfactorily adjust photographic image composition without special operations before the main light emission and image data acquisition are performed in steps S 313  and S 314 . Next, the photographic mode program returns to step S 302  for the repetitive operation.  
         [0032]     Hereinafter, a photographic mode program performed by the central processing device  1  according to a third embodiment of the present invention will be described with reference to  FIGS. 1 and 4 . In the third embodiment, the shutter signal is detected only once, allowing for fast and convenient operation.  
         [0033]     The central processing device  1  initializes itself and other elements involved in photographic operations in step S 401 . When the current operation mode is determined to be a photographic mode in step S 402  and when a shutter signal is received from the shutter button switches SS in step S 403 , ambient illumination is measured in step S 404 .  
         [0034]     Next, when the measured ambient illumination is greater than or equal to a second reference value, for example, “9”, in steps S 405   a  and S 405   b , image data is acquired and processed by the photographic unit  2  in step S 414  without performing preliminary light emission and main light emission. Next, the photographic mode program returns to step S 402 , allowing repetitive operation.  
         [0035]     However, when the measured ambient illumination is less than the second reference value and greater than or equal to a first reference value, for example, “3”, in steps S 405   a  and S 405   b , only the main light emission without the preliminary light emission is performed because the measured ambient illumination is sufficient for a user to adjust image composition while the main light emission is still required to obtain an image file. More specifically, when the capacitor MC has not been completely charged in step S 4071   b , the capacitor MC is charged by the strobe driver  5  in step S 408   b . Next, the strobe lamp XE is turned on by the strobe driver  5 , thereby performing the main light emission in step S 413 . Next, image data is acquired by the photographic unit  2  in response to the main light emission in step S 414 . Next, the photographic mode program returns to step S 402 , allowing repetitive operation.  
         [0036]     However, when the measured ambient illumination is less than the first reference value in step S 405   a , the following steps are performed.  
         [0037]     When the capacitor MC has not been completely charged in step S 407   a , the capacitor MC is charged by the strobe driver  5  in step S 408   a . Next, the strobe lamp XE is turned on by the strobe driver  5 , thereby performing the preliminary light emission in step S 409 . Next, a 3-second timer is started in step S 410 . When a timer end signal is received after three seconds in step S 411 , the strobe lamp XE is turned on by the strobe driver  5 , thereby performing the main light emission in step S 413 . Next, image data is acquired by the photographic unit  2  in response to the main light emission in step S 414 . Thus, under low illumination, the user can satisfactorily adjust photographic image composition, without special operations, before the main light emission and image data acquisition are performed in steps S 413  and S 414 . Next, the photographic mode program returns to step S 402 , allowing repetitive operation.  
         [0038]     Although a few embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that changes may be made in these elements without departing from the spirit and scope of the invention, the scope of which is defined in the appended claims and their equivalents.