Abstract:
An electronic still camera is described which allows previewing the composition of an image before the image is stored. The digital still camera includes at least two release switches; a lens unit; an image pickup unit for converting the optical image into corresponding electronic image data; a controller responsive to the settings of the release switches and outputting either static image data or moving image data in real time; a first memory device for temporarily storing the static image data received from the controller; and a display unit for displaying either the static image corresponding to the static image data or the moving image corresponding to the moving image data, as determined by the controller.

Description:
BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a digital still camera, and more particularly, to a digital still camera which allows previewing the composition of an image before the image is stored. 
     (b) Description of the Related Art 
     An electronic camera generally uses an image pickup device such as a color CCD (Charge Coupled Device) instead of a film when acquiring an image of an object. The output of the image pick-up device is converted into electrical signals which are recorded in a memory device. In a video camera, the memory device is a typically magnetic tape, and in a digital still camera, the memory device is typically an IC (Integrated Circuit) or a floppy disk. 
     The digital still camera has a photographic lens system and often uses Liquid Crystal Display (LCD) which displays either a still image of the object or a moving image in real time. A user can then view the static image or the moving image on the LCD. 
     When the image of an object is taken by either of the methods described above, a user knows the exact composition of the photographed image only after the corresponding image data, which are recorded in the memory device, are displayed on the LCD or on a computer monitor. If the user finds the composition of the photographed image unacceptable, the user must be able to delete the stored image data. The user can then take another image of the object until he is satisfied with the composition of the image. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a digital still camera and a method, where the composition of an image can be previewed before the image is recorded in the memory device. 
     The object of the invention is achieved by a digital still camera which includes at least two release switches. The digital still camera further includes a lens unit for capturing an optical image of the object; an image pickup unit for converting the optical image into corresponding electronic image data; a controller, responsive to the settings of the release switches, outputting either static image data or moving image data; a temporary memory device for temporarily storing the static image data received from the controller; and a display unit for displaying either the static image corresponding to the static image data or the moving image corresponding to the moving image data, as determined by the controller. 
     The method of the invention includes the steps of determining whether or not a first release switch is activated; if the first release switch is activated, storing the static image data in the temporary memory device, and displaying the static image on the display unit; or if the first release switch is not activated, deleting the static image data stored in the temporary memory device and displaying the moving image data in real time on the display unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and features of the present invention will be apparent from the following description of the preferred embodiments with reference to the accompanying drawings. 
     FIG. 1 is a block diagram of a controller of a digital still camera for previewing the composition of an image in accordance with a first embodiment of the present invention; 
     FIG. 2 is a flow chart illustrating a method for previewing the composition of the image of FIG. 1; 
     FIG. 3 is a block diagram of the controller of the digital still camera for previewing the composition of an image in accordance with a second embodiment of the present invention; and 
     FIGS. 4A and 4B are flow charts illustrating a method for previewing the composition of the image of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     A first preferred embodiment according to the present invention will be explained referring to FIGS. 1 and 2. 
     In FIG. 1, reference number  10  refers to an object and reference number  20  refers to a lens unit capturing the reflected-light image from the object  10 . 
     Reference number  30  refers to an image pick-up unit (CCD) which receives the optical image captured by the lens unit  20  and generates electrical analog image signals corresponding to the optical image. Reference number  40  refers to an analog/digital converter which is connected to the output terminal of the image pick-up unit  30 . The analog/digital converter  40  converts the analog image signals to digital image signals. 
     Reference number SW 1  is a first release switch and SW 2  is a second release switch. Both switches are operated by a user. 
     Reference number  50  refers to a controller. The controller  50  is connected to the output terminal of the analog/digital converter  40  and to output terminals of the first and second release switches SW 1  and SW 2 . 
     Reference number  60  refers to a display unit, such as a LCD, which is connected to a first output terminal of the controller  50  and displays either a static image or a moving image in real time. 
     Reference number  70  refers to a temporary memory device which is connected to a second output terminal of the controller  50  and which temporarily stores static image data received from the controller  50 . Reference number  80  refers to a main memory device which is connected to a third output terminal of the controller  50  and which stores compressed static image data after compression by the controller  50 . 
     Referring now also to FIG. 2, the digital still camera according to the first embodiment of the present invention operates follows: 
     The controller  50  initializes a digital still camera in step S 10  and reads a signal outputted from the first release switch SW 1  to determines its state, i.e., if the switch SW 1  has been activated by the user or not, steps S 11  and S 12 . 
     A high level signal H received by the controller  50  from the first release switch SW 1  indicates that the first release switch SW 1  is not activated, in which case the controller  50  stops the output of the static image data to the display unit  60  and switches to output the moving image data in real time. The static image data correspond to the static image which is acquired when the first release switch SW 1  is activated. 
     Conversely, a low level signal L received by the controller  50  from the first release switch SW 1  indicates that the first release switch SW 1  is activated by the user, in which case the controller  50  controls the exposure conditions (focusing, exposure settings) (not shown) of the digital still camera. When the first release switch SW 1  is activated, the static image is captured and converted into the static image data. The static image data are inputted into the analog/digital converter  40 ; the converted digital data are then sent to the controller  50  which in turn outputs the data to both a temporary memory device  70  for storage and to the display unit  60  for previewing, step S 13 . 
     If the first release switch SW 1  is activated, the static image is displayed on the display unit  60 ; the user can then preview a composition of the static image (step S 14 ) before the image is stored in a main memory device  80 . If the user finds the composition of the static image displayed on the display unit  60  acceptable, the user activates the second release switch SW 2  to record the displayed static image in the main memory device  80 . 
     If, on the other hand, the user finds the composition of the static image unacceptable, the user can release the first release switch SW 1 . The display unit  60  will then again display the moving image, step S 110 . 
     The controller  50  then reads a signal outputted from the second release switch SW 2 , and determines whether or not the second release switch SW 2  is activated by the user, steps S 15  and S 16 . 
     A low level L received from the second release switch SW 2  by the controller  50  indicates that the second release switch SW 2  is activated by the user. The controller  50  then compresses the static image data recorded in the temporary memory device  70  and stores the compressed static image data in the main memory device  80 . The controller  50  also deletes the static image data which are recorded the temporary memory device  70 , step S 17 . 
     Conversely, when the second release switch SW 2  is not activated by the user, the controller  50  outputs the static image data which are recorded in the temporary memory device  70 , to the display unit  60 . In the default setting, i.e. when the first release switch SW 1  and the second release switch SW 2  are not activated, the display unit  60  displays the static image corresponding to the static image data. 
     In step S 18 , the controller  50  detects if the first release switch SW 1  is released again after being activated, in which case the controller  50  deletes the static image data recorded in the temporary memory device  70 , step S 19 , and stops the output of the static image data to the display unit  60 , step S 110  The controller  50  then outputs to the display unit  60  the moving image data instead of the static image data. 
     However, if the release switch SW 1  is activated in step S 18 , the controller  50  outputs to the display unit  60  the static image data recorded in the temporary memory device  70 . 
     The user can then preview the composition of the static image and if he finds the composition of the static image acceptable, record the displayed static image in the main memory device by activating the second release switch SW 2 . 
     FIGS. 3 and 4 illustrate a digital still camera according to the second embodiment of the present invention. 
     As shown in FIG. 3, a control apparatus of a digital still camera capable of previewing a composition of a photograph in accordance with the second preferred embodiment of the present invention This camera has similar features s as the camera of the first embodiment of FIG. 1, expect for an additional composition locking switch SW 3  which is connected to the controller  51  of FIG.  3 . 
     The camera in accordance with the second embodiment of the present invention operates as follows: 
     A controller  51  initializes the digital still camera in step S 20  and reads a signal outputted from the first release switch SW 1  to determine its state, i.e., if the switch SW 1  has been activated by the user or not, steps S 21  and S 22 . 
     A high level signal H received by the controller  51  from the first release switch SW 1  indicates that the first release switch SW 1  is not activated, in which case the controller  51  outputs to the display unit  60  the moving image data instead of the static image data. 
     Conversely, a low level signal L received by the controller  51  from the first release switch SW 1  indicates that the first release switch SW 1  has been activated, in which case the controller  51  controls the exposure conditions (focusing, exposure settings) (not shown) of the digital camera . The controller  51  also reads a signal outputted from the composition locking switch SW 3  to determine its status, i.e., whether or not the composition locking switch SW 3  is activated, steps S 23  and S 24 . 
     If the composition locking switch SW 3  is activated, the controller  51  controls the digital still camera to output a static image on the display unit  60  while the first release switch SW 1  is activated. 
     Also, the controller  51  determines whether or not status of the first release switch SW 1  has changed, i.e., whether the first release switch SW 1  has been deactivated or reactivated, because such change could have changed the static image data recorded in the temporary memory device  70 , step S 25 . 
     If the controller  51  determines that the first release switch SW 1  has been reactivated while the composition locking switch SW 3  is activated, then the controller  51  stores the new static image data, captured after reactivation of release switch SW 1 , in the temporary memory device  70  and also outputs the new static image data to the display unit  60 , steps S 26  and S 27 . 
     The user can thus preview the composition of the new static image before the image new static image is recorded in the main memory device  80 . 
     If the status of the first release switch SW 1  is unchanged, step S 25 , then the static image also did not change and the controller  51  outputs to the display unit  60  the static image data recorded in the temporary memory  70 . 
     Accordingly, with the composition locking switch SW 3  activated, the controller  51  can output to the display unit  60  either the previous static image data or, alternatively, the new static image data depending on whether the first release switch SW 1  has been reactivated or not. 
     If the user finds the composition of the displayed static image acceptable, he activates the second release switch SW 2  to record the static image in the main memory device  80 . Conversely, if the user finds the composition of the static image unacceptable, there is no need to store the static image in main memory  80 . Accordingly, the controller  51  reads the signal outputted from the second release switch SW 2 , step S 28 , and determines whether or not the second release switch SW 2  is activated, step S 201 . 
     If the composition locking switch SW 3  is deactivated, step S 24 , the digital camera of the second embodiment operates like that of the first embodiment. The controller  51  then outputs to the display unit  60  the moving image, step S 29 ; the controller  51  also determines whether or not the second release switch SW 2  is activated, steps S 28  and S 201 . 
     A low level signal L received by the controller  51  from the second release switch SW 2  indicates that the second release switch SW 2  is activated in which case the controller  51  compresses the static image data recorded in the temporary memory device  70  and transfers the compressed static image data to the main memory device  80 . The static image data recorded in the temporary memory device  70  are subsequently deleted, steps S 204  and S 205 . 
     Conversely, if the second release switch SW 2  is not activated, the controller  51  continues to output to the display unit  60  the static image data recorded in the temporary memory device  70 . The displayed static image corresponds to the image data obtained when the first release switch SW 1  was activated. The controller  50  determines in step S 202  whether or not the first release switch SW 1  is activated. 
     If the first release switch SW 1  is deactivated, the static image data recorded in the temporary memory device  70  are deleted, step S 204 , and are no longer transmitted to the display unit  60 , step S 206 . The display unit  60  then displays a moving image. 
     Conversely, if the first release switch SW 1  is activated, step S 203 , the controller  51  returns to step S 23  and reads the signal outputted by the composition locking switch SW 3 , step S 23 . 
     With a digital still camera of the present invention, the user can preview and select a preferred composition of an image before recording the image in the main memory device, saving time and money. 
     Furthermore, the user can make more efficient use of the memory device because only acceptable images are recorded. 
     The camera is also more convenient to operate because the user can “lock” an acceptable image and store that image in the main memory device by activating the composition locking switch. 
     While it has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications can by readily made therein without departing from the scope and sprit of the invention as defined by the appended claims.