Abstract:
A system and a method for flat panel display brightness correction, removing brightness difference between flat panel displays in one product line. The brightness correction system comprises a converter for control of color temperature and brightness of an image frame, and a backlight controller for generating corrected light for display in the image frame.

Description:
BACKGROUND  
       [0001]     The invention relates to flat panel display, and in particular, to brightness correction for flat panel displays.  
         [0002]      FIG. 1  shows a conventional flat panel display architecture. A digital signal  102  is received by a timing controller  104 , transformed to an image signal and control signal, and input to line controller  108  and row controller  110 , whereby a visual output is displayed on display panel  106  under scan line synchronization control. Timing controller  104  is an Application Specific Integrated Circuit (ASIC) controlling the display panel  106 , and the inverter  112  is capable of generating high voltage to drive the backlight module in the display panel  106 . The backlight module (not shown) are tubes, LED or plasma cells cooperating with light guides and diffusion films to light the display panel  106 . Based on the light provided, and pixel control techniques, color variations of an image can be presented as visual output on display panel  106 . The relationship between the input signal and visual output, however, is not linear but exponential, referring to “gamma curve”. Therefore gamma correction is implemented by resistors in the row controller  110  to display the visual output correctly.  
         [0003]     Another issue occurs when implementing flat panel displays. Among a plurality of panels within one product line, the physical characteristics are not completely identical, causing brightness not to be uniform when driven in the same condition. The variation is increased after gamma correction, white balance and color temperature compensation. To achieve brightness uniformity, a brightness correction mechanism is desirable. Conventionally, a display panel having the lowest brightness is selected as a reference and brightness of other display panels is reduced according thereto. The display efficiency is derived as follows: 
 
Efficiency=brightness/(voltage*current) 
 
         [0004]     If brightness is reduced by gamma correction, efficiency is decreased, resulting in undesirable power consumption. Therefore an improved method is desirable.  
       SUMMARY  
       [0005]     An embodiment provides a flat panel display comprising a timing controller, a converter, a memory device, a backlight controller, and a display panel. A digital signal is generated by the timing controller based on a control signal. An image signal is transformed to a corresponding output signal by the converter. A brightness parameter is stored in the memory device. A brightness control signal is generated according to the brightness parameter by the backlight controller. The brightness control signal is received by an inverter to generate a corresponding current. The display panel receives the output signal to generate a visual output, and receives the current to brighten the visual output.  
         [0006]     The converter is an arithmetic circuit, providing gamma correction, white balance or color temperature compensation. The memory device is Electrically Erasable Programmable Read-Only Memory (EEPROM) or FLASH ROM. The display panel comprises a column driver and a row driver. The image signal is received from the converter by the column driver to generate the visual output. The row driver receives the control signal to synchronize scan lines.  
         [0007]     Another embodiment provides a brightness correction method for flat panel display, comprising the following steps. First, a plurality of flat panel displays is driven based on a selected condition. Brightness of the flat panel displays is then determined. The lowest brightness is chosen therefrom, and corresponding brightness parameters for each flat panel display are calculated accordingly. Flat panel displays controlled by corresponding brightness parameters thus have equal brightness when driven under the same conditions.  
         [0008]     The configuration of the selected condition comprises the following steps. First, white balance for each flat panel display is processed, such that the color temperatures thereof are equal. A selected voltage or current is provided to drive the flat panel displays to display full white screens. Brightness determination comprises determining brightness of each full white screen, such that the lowest brightness can be obtained. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The following detailed description, given by way of example and not intended to limit the invention solely to the embodiments described herein, will best be understood in conjunction with the accompanying drawings, in which:  
         [0010]      FIG. 1  shows a conventional flat panel display architecture;  
         [0011]      FIG. 2  shows an embodiment of a flat panel display;  
         [0012]      FIG. 3  is a flowchart of brightness correction; and  
         [0013]      FIG. 4  shows brightness level of flat panel displays. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]      FIG. 2  shows an embodiment of a flat panel display. The timing controller  104 , display panel  106 , line controller  108  and row controller  110  are identical to the conventional flat panel display in  FIG. 1 . In addition, a memory device  202 , backlight controller  204 , converter  206  and inverter  212  are provided. The converter  206  comprises a lookup table (not shown) implemented by an arithmetic circuit or digital component, capable of transforming input values into corresponding output values. After a digital signal  102  is received by the converter  206 , the lookup table performs color temperature compensation, white balance and gamma correction for the digital signal  102 , and an image signal is then output to the row controller  110 . The timing controller  104  receives the digital signal  102  and output a control signal to the line controller  108  for scan line synchronization. A backlight controller  204  is provided for outputting a brightness control signal to the inverter  212  after the brightness parameters in the memory device  202  is read, such that the brightness presented on the display panel  106  is corrected. The inverter  212  is capable of adjusting the output current or output duty cycle according to the brightness control signal, and the brightness of the display panel  106  is tuned accordingly. A pixel map of the visual output is generated by the row controller  110 , and the inverter  212  determines the brightness of the visual output. The line controller  108  receives the control signal for scan line synchronization. Based on the architecture, display efficiency remains unaffected because power consumption is proportionally decreased by adjusting the inverter  212 .  
         [0015]     The inverter  212  can be a Pulse Width Modulation (PWM) inverter, wherein the brightness is proportional to the duty cycle of current. The memory device  202  can be an EEPROM or EFPROM, storing brightness parameters configured in the manufacture stage. The backlight controller  204  and converter  206  can be independent circuit components, or implemented in the timing controller  104 . The backlight controller  204  and converter  206 , performing gamma correction, white balance and color temperature compensation, are capable of transforming the digital signal  102  to an image signal based on specific lookup tables configured at manufacture stage such as gamma curve, and generating visual output on display panel  106  via row controller  110 . The specific lookup tables are stored in memory device  202 , thus is flexible to program.  
         [0016]      FIG. 3  is a flowchart of brightness correction. Specific driving conditions are defined, and characteristics of all flat panel displays can be measured under the same driving condition. For example, the flat panel displays can receive identical brightness control signals, and identical white balance parameters. In step  302 , the brightness of each flat panel display under the same driving condition is measured. In step  304 , the lowest brightness is chosen as a reference, and in step  306 , brightness parameters of each flat panel display are calculated by comparison with the lowest brightness and then stored in the memory device  202 . In step  308 , the brightness parameter is read by the backlight controller  204 , and a corresponding backlight control signal is generated to control the inverter  212  and generate a current to drive the flat panel display with corrected brightness.  
         [0017]     Measurement of brightness under the specific driving conditions comprises the following steps. First, at least one of the following steps is performed on each display panel: gamma correction, white balance and color temperature compensation. Thereafter, the brightness of each display panel is measured.  
         [0018]      FIG. 4  shows brightness level of a plurality of flat panel displays. Under specific driving conditions, each display panel presents different brightness, and in the embodiment of  FIG. 3 , the lowest brightness is chosen as a reference, for example, LCD7, whereby all other display panels are reduced accordingly to achieve brightness uniformity among the plurality of flat panel displays.  
         [0019]     While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited thereto. Rather, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.