Abstract:
A digital camera includes a LCD that has a back light whose intensity level is set at a point midway between a maximum intensity setting and a minimum intensity setting. The back light level is then adjusted automatically from this default setting to a brightness level that corresponds to a measured scene level. The back light intensity level and contrast level of the LCD then change automatically thereafter to correspond to the measured scene level whereby the LCD controls are adjusted according to the lighting environment.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a illuminated display unit and method of using the display and more particularly relates to a method of using a liquid crystal display unit in a digital camera under a variety of photographic lighting conditions.  
       BACKGROUND ART  
       [0002]     In modern day digital cameras, the viewing of the scene that will be captured is accomplished with either an optical viewfinder or a liquid crystal display (LCD) unit either alone or in combination with an optical viewfinder. In most, if not in all digital cameras, the intensity level or brightness level of the LCD is manually adjustable to accomodate for standard photographic lighting conditions. That is a middle of the road approach is taken to accomodate for both indoor and outdoor lighting conditions.  
         [0003]     Besides the viewing of a scene with the LCD, the LCD also accomplishes two other primary purposes by displaying menu selections for enabling the user to control or set up camera operating conditions, and to display camera status information whenever a user is ready to capture an object image or has in fact captured an object image. While the LCD is able to perform these various function in general lighting conditions, all too often due to overly bright or dim ambient light conditions, the image displayed on the LCD is either too bright or too dim thereby greatly hindering a user in properly operarting the camera.  
         [0004]     One attempt at solving this problem has been to provide an over-riding manual adjustment to control the backlighting of the LCD. While this approach is satisfactory in some lighting conditions, the solution has not been entirely satisfactory. In this regard, the control selection for over-riding the default backlighting condition is generally found in a buried camera menu item that must be display on the LCD. Since the menu selection item must be displayed to be selected, often times it is difficult or entirely impossible to display the menu item so that it may be clearly viewed by a user due to the ambient lighting conditions.  
         [0005]     Therefore it would be highly desirable to have a new and improved digital camera that includes an LCD that operates in a variety of photographic lighting conditions ranging from poorly illuminated indoor settings to brightly illuminated outdoor settings.  
       SUMMARY OF THE INVENTION  
       [0006]     A digital camera includes a LCD that has a back light level that is set at a point midway between a maximum intensity setting and a minimum intensity setting. The back light level is then adjusted automatically from this default setting to a brightness level that corresponds to a measured scene level. The back light intensity level then and contrast level are changed automatically thereafter to correspond to the measured scene level. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The above mentioned features of the present invention and the manner of attaining them will become apparent and the invention itself will be best understood by reference to the following description of the preferred embodiment of the invention, in conjunction with the accompanying drawings, wherein:  
         [0008]      FIG. 1  is a block diagrammatic representation of the digital camera of  FIG. 1 ;  
         [0009]      FIG. 2  is a pictorial view of a digital camera which is constructed in accordance with the preferred embodiment of the present invention;  
         [0010]      FIG. 3  is high level flowchart of a control algorithm utilized to help set the brightness level setting of the LCD forming part of the digital camera of  FIG. 1 ; and  
         [0011]      FIG. 4  is a high level flowchart of a determination algorithm to calculate the brightness level of the LCD forming part of the digital camera of  FIG. 1 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]     Referring now to the drawings and more particularly to  FIGS. 1-2  thereof there is shown a digital camera  10  which is constructed in accordance with the present invention. The digital camera  10  is a portable device that operates in a variety of lighting conditions ranging from poorly illuminated indoors lighting situations to brightly illuminated outdoors lighting situations.  
         [0013]     Considering the camera  10  in greater detail with reference to  FIGS. 1-2 , the camera  10  generally includes a housing  16  having mounted therein a lens system or arrangement  13  that helps facilitate directing the light reflecting from an object to be captured to the photosensitive plane of the camera  10 . In order to help a user frame the object to be captured, the camera  10  also includes an optical viewfinder  14  having a dichroic mirror  43  and a status indicator  44  that enables a user to visualize a through the lens scene while simultaneously viewing status information regarding the camera  10 .  
         [0014]     In order to help limit the amount of light that is communicated to the photosensitive plane of the camera, the camera  10  further includes an aperture  18  that is automatically adjusted by a microprocessor  25  via a stepper motor  29 . In this regard, the stepper motor  29  is coupled electrically to the microprocessor  25  and coupled mechanically to the aperture  18  in order to facilitate receiving the proper amount of light to assure proper image formation.  
         [0015]     As best seen in  FIG. 1 , a shutter  19  is sandwiched between the aperture  18  and the photosensitive plane of a charged couple device (CCD)  15  that converts light into an electrical signal that is indicative of the object framed within the optical viewfinder  14 . The shutter  19  is also coupled to the stepper motor  29  to further facilitate controlling the amount of light that is allowed to fall on the CCD  15  for light converting purposes. To help control the strength of the electrical signal passing from the CCD  15  to the microprocessor  25 , the camera  10  further includes a gain control device, such as an variable gain operational amplifier  47 , whose output is connected to an analog to digital converter  48 . The analog to digital converter  48  converts the analog signal passing from the output of the gain control device  47  into a digital signal of an acceptable level for processing by the microprocessor  25 . A digital to analog converter  58  is coupled electrically between the microprocessor  25  and the gain control  47  to enable the microprocessor  25  to control the strength of the output signal that will be converted by the analog to digital converter  48 . As will be explained hereinafter in greater detail, the microprocessor  25  operates under a set of control programs that are stored in an internal memory device, such as random access memory (RAM) module  84 .  
         [0016]     The digital camera  10  further includes a memory controller  52  that operates under the control of the microprocessor  25  for facilitating the permanent storage of each object image captured by the camera  10 . In this regard, the memory controller  52  is adapted to receive a removable memory card  56  that functions to store the object images captured by the camera  10 .  
         [0017]     In order to enable the user to visualize images in either a live view mode of operation or in a review mode of operation ( relative to images previously stored on the removable memory card  56 ), the digital camera  10  also includes a display unit, such as a liquid crystal display (LCD) unit  38 . The LCD  38  is coupled to the microprocessor  25  via an internal bus  26  which also allows for buffering of images to the LCD  38  from a set of internal buffer registers forming part of the microprocessor  25 . The LCD  38  has a backlight  39  that is controlled by an LCD brightness/contrast control program  300  that will be described hereinafter in greater detail. For the moment it will suffice to indicate that the blacklight level of the LCD  38  is controlled to correspond to a measure ambient light level that is determined during the auto-exposure sequencing of the camera  10 .  
         [0018]     The digital camera  10  further includes a user interface  17  having a set of control switches that includes a power on/off switch  26 , a mode selection switch  28 , a zoom in switch  30 , a zoom out switch  32  a live view switch  34  and a shutter actuation switch  36 . The function of each of the switches will be described hereinafter in greater detail where relative.  
         [0019]     Considering now the LCD brightness/contrast control program  300  in greater detail with reference to  FIG. 3 , the control program  300  begins whenever the user actuates the power switch  26 . In this regard, the control program begins at a start command  302  and proceeds to a command step  304  that sets a POWER OFF flag equal to a logical zero.  
         [0020]     From the command step  302 , the program advances to a command step  306  that sets the LCD CONTRAST  to a default contrast level DEFAULT CONTRAST . Next the program proceeds to a command step  308  that sets the LCD BRIGHT  to a default brightness level DEFAULT BRIGHT . From the foregoing it should be understood by those skilled in the art, that the brightness level and the contrast level of the LCD  38  are set to default levels which are located between maximum and minimum levels.  
         [0021]     After the command step  308  is executed, the program goes to a decision step  310  to determine whether the user has placed- the camera  10  in the capture mode of operation using the mode selection switch  28 . If this condition is true, the program goes to a command step  350  ( FIG. 3B ) that will be described hereinafter in greater detail. If this condition is not true, the program advances to a decision step  312  to determine whether the user has placed the camera  10  in a review mode of operation utilizing the mode selection switch  28 .  
         [0022]     If a determination is made at decision step  312  that the camera  10  is operating in a review mode of operation, the program proceeds to a decision step  323  ( FIG. 3C ) that will be described hereinafter in greater detail. Otherwise, the program advances to a decision step  314  to determine whether the user has placed the camera in a connect mode of operation using the mode selection switch  28 . If the user has not actuated the mode selection switch  28  to place the camera  10  in the connect mode of operation, the program proceeds to a decision step  318  to determine whether the user has actuated the power switch  26  to power down the camera  10 .  
         [0023]     If the user has actuated the power switch  26 , the program goes to an exit command step  321  and exits the subroutine  300 . If the user has not actuated the power switch  26 , the program proceeds to a decision step  319  to determine whether the internal time out period of the camera  10  has elapsed. If the time out period has elapsed, the program goes to the exit command  321  and proceeds as described previously. Otherwise, the program advances to the decision step  310  and continues as described previously.  
         [0024]     Considering again the decision step  314 , if the user has placed the camera  10  in the connect mode of operation, the program advances to a command step  311  that causes the LCD contrast level to be set equal to the default contrast level. Next the program continues to a command step  313  that causes the LCD brightness level to be set to the default brightness level.  
         [0025]     The program then advances to a command step  315  that sets up the brightness level to use the LCD setting when displaying messages on the LCD  38 .  
         [0026]     From the command step  315  the program proceeds to a determination step  316  to determine whether the camera  10  is busy. If the camera  10  is not busy, the program goes to a command step  317  that will be described hereinafter in greater detail. Otherwise, if the camera  10  is busy, the program returns to step  315  and proceeds as described previously.  
         [0027]     From the foregoing, it should be understood that the default setting for the LCD are activated at the command step  315  for displaying messages on the LCD  38 . The program then proceeds from the command step  315  to to a command step  317  that causes the POWER OFF  flag to be set to a logical zero. After setting the POWER OFF  flag, the program continues to the decision step  318  and proceeds as described previously.  
         [0028]     Considering now the command step  350  in greater detail with reference to  FIG. 3B , the command step  350  set a back light on value (LV ON ) to a logical zero, live view is off, a loop maximum flag to a logical zero, and a loop flag to a logical zero. LV ON  indicates the status of the live view mode where LV ON =1 is active and LV ON =0 is inactive. The term LOOP MAX  means skip n number of frames in the live view mode before recalculating the display settings. In this regard, the typical frame rate in the live view mode is about 30 frames per second. Therefore LOOP MAX  would be selected to be 15 frames so the brightness and contrast would be adjusted twice per second. More specifically it is not necessary to update the display settings in the live view mode in each frame as the scene brightness does not change that rapidly.  
         [0029]     After execution of command step  350 , the program proceeds to a call command step  352  that causes an auto-exposure subroutine to be executed, such as the auto exposure subroutine described in U.S. patent application Ser. No. ______. After the auto-exposure subroutine is executed, the program returns to the step, a decision step  354  to determine whether the user has utilized the mode selection switch  28  to place the camera  10  in other than the capture mode of operation. If this condition is true, the camera advances to a command step  355  that causes the LCD unit  38  to turn off in order to conserve camera power. After executing command step  355  the camera goes to decision step  318  and proceeds as described previously.  
         [0030]     If at decision step  354  a determination is made that the camera  10  is still operating in the capture mode of operation, the program advances to a decision step  356  to determine whether the user has activated the live view mode switch  34 . If a determination is made that the user has activated the liveview switch  34 , the program goes to a decision step  358  that will be described hereinafter in greater detail. Otherwise the camera goes to a decision step  357  to determine whether if live view is currently on. If LV ON  has been set to logical one level, the program proceeds to a command step  362  that will be described hereinafter in greater detail. Otherwise, the program goes to a call step  365  that causes the auto-exposure subroutine to be called.  
         [0031]     After the auto-exposure subroutine has been executed the program returns and EV value and continues to a decision step  367  to determine whether the user has actuated the shutter switch  36 . If the shutter switch  36  has not been actuated, the program returns to the decision step  354  ( FIG. 3B ) and proceeds as described previously. If the shutter switch  36  has been actuated, the program advances to a command step  368  that turns power off of the LCD  38  in order to preserve camera power. Once command step  368  is executed the program proceeds to a command step  370  that causes the CCD  15  to capture the object image framed by the viewfinder  14 .  
         [0032]     Once the object image has been captured, the program goes to a process command step  372  that causes the microprocessor  25  to process the captured image for storage purposes. Next the program goes to a store command step  374  that causes the processed image to be stored on the removable memory device  56 . After the image is stored, the program advances to a command step  376  that causes the POWER OFF  flag to be set to a logical one level. It should be understood by those skilled in the art that after an image is captured and then reviewed there is no immediate need to change the display settings. On the other hand, if the user is reviewing stored images while POWER OFF =0 then base the display settings on the image settings when the image was originally captured. The program then returns to the decision step  354  and proceeds as described previously.  
         [0033]     Considering now the decision step  358  in greater detail with reference to  FIG. 3B , if LV ON  is not set to a logical one, the program proceeds to a command step  359  that cause the LCD display unit to be activated. It should be understood that at step  358  since the liveview (LV) switch has been activated, LV will switch to the opposite state (off if on, on if off). Next the program proceeds to a command step  360  that set LV ON  to a logical one. The program then proceeds to command step  362  that will be described hereinafter in greater detail. If at step  358  LV ON  is set to a logical one, the program goes to a command step  363  that causes LV ON  to be reset to a logical zero. From command step  363  the program goes the call step  365  and proceeds as described previously.  
         [0034]     Considering now the command step  362  in greater detail with reference to  FIG. 3B , the command step  362  causes the loop counter LOOP to be incremented by one. That is LOOP is set equal to LOOP+1. Next, the program continues to a decision step  364  to determine whether the LOOP counter is less than a maximum loop value LOOP MAX . If this condition is not true, the program advances to a command step  384  ( FIG. 3B ) that will be described hereinafter in greater detail. If the condition is true, the program proceeds a command step  366  that set LOOP equal to a logical zero. Next the program advances to a call command  371  that causes a LCD setting subroutine  400  to be executed as will be described hereinafter in greater detail. After the subroutine  400  is executed the program returns and continues to a command step  373  that set the contrast level of the LCD  38  equal to a current LCD CONTRAST  level and sets the LCD BRIGHT  level to the current brightness level. The program then advances to a command step  384  ( FIG. 3B ) that will be described hereinafter in greater detail.  
         [0035]     Considering now the command step  384  in greater detail with reference to  FIG. 3B , the command step  384  causes a live view image to be captured. The captured live view image is then processed or subsampled at a command step  386 . Next, the program advances to a command step  388  that causes the captured and processed live view image to be displayed on the LCD  38 . The program then goes to call command  365  and proceeds as described previously.  
         [0036]     Considering now the decision step  323  as advanced to from decision step  312  in greater detail with reference to  FIG. 3C , the decision step  323  determines whether the POWER OFF  flag has been set to a logical one. If this condition is not true, the program goes to a command step  325  that causes the microprocessor  25  to access a file header and then retrieve from the file the EV value. Once the command step  325  has been executed the program goes to a call command  327  that calls the LCD setting subroutine  400  that will be described hereinafter in greater detail. After the subroutine  400  is executed, the program returns and continues to a command step  329  that will be described hereinafter in greater detail.  
         [0037]     If a determination is made at decision step  323  that the POWER OFF  flag is set to a logical one (indicating that power was not turned off between capturing an image and review the image), the program advances to the command step  329 . Command step  329  sets the LCD brightness and contrast levels to LCD BRIGHT  and LCD CONTRAST  respectively. Next, the program goes to a command step  331  that set the illumination level of the status indicator  44  to its default level. From step  331  the program proceeds to a command step  332  that causes the status indicator  44  to blink to provide and indication to the user that the camera  10  is busy processing an image.  
         [0038]     Next the program goes to a command step  333  that causes the microprocessor  25  to retrieve an image file and decompress the image for display purposes. In this regard, after the image has been decompressed the program goes to a command step  335  that causes the decompressed image to be displayed on the LCD  38 . The program then returns to step  318  ( FIG. 3A ) and proceeds as described previously.  
         [0039]     Considering now the LCD setting subroutine  400  in greater detail with reference to  FIG. 4 , the subroutine is executed in response to the call commands at steps  327  ( FIG. 3C ) or  371  ( FIG. 3B ) respectively. After the subroutine  400  is executed the program returns to the next step following the call command that caused the subroutine  400  to commence. In any event, the subroutine  400  begins at a start command  401  and proceeds to a command step  402  that causes EV LCD  to be set to EV. Next the program advances to-a decision step  404  to determine whether EV is greater than EV MAX . If this condition is determined, the program proceeds to a command step  414  that sets EV LCD  to EV MAX . The program then goes to a command step  408  that will be described hereinafter in greater detail.  
         [0040]     If a determination is made at decision step  404  that EV is not greater than EV MAX , the program proceeds to a decision step  406  to determine whether EV is less than EV MIN . If this condition is determined, the program goes to a command step  416  that causes EV LCD  to be set to EV MIN . After setting the EV value to the minimum value the program proceeds to the command step  408 . If a determination is made at decision step  408  that EV is not less than the EV MIN  then the program goes directly to the command step  408 .  
         [0041]     Considering now the command step  408  in greater detail, the command step  408  causes the LCD CONTRAST  to be set to a default value or DEFAULT CONTRAST . Next the program goes to a command step  410  that sets the LCD BRIGHT  level equal to (16* EV LCD −32) in order to map EV into a digital word representing the LCD BRIGHT . The program then goes to a decision step  412  to determine whether LCD BRIGHT  is equal to or greater the maximum brightness level or BRIGHT MAX .  
         [0042]     If a determination is made at step  412  that LCD BRIGHT  is greater than or equal to the maximum brightness level the program advances to a command step  418  that set LCD CONTRAST  equal to (16*EV LCD −32). This value is selected since the LCD backlight brightness level is at maximum and the only way to increase apparent display brightness is to decrease the display contrast; i.e. the more washed out colors displayed appear brighter on the LCD  38 . The program then goes to a return command  420  that returns the program to the subroutine  300  as mentioned earlier.  
         [0043]     While particular embodiments of the present invention have been disclosed, it is to be understood that various different modifications are possible and are contemplated within the true spirit and scope of the appended claims. There is no intention, therefore, of limitations to the exact abstract or disclosure herein presented.