Patent Publication Number: US-2009219306-A1

Title: Luminance correction system and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of Korean Patent Application No.10-2008-0018311, filed on Feb. 28, 2008, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a luminance correction system and method, and more particularly to a luminance correction system and method to reduce time required for luminance correction by using a stored lookup table. 
     2. Description of Related Art 
     An organic light emitting display displays an image using an organic light emitting diode (OLED) generating light by the recombination of an electron and a hole. 
     The organic light emitting diode includes an anode electrode, a cathode electrode, and a light emitting layer positioned therebetween. If current flows in a direction from the anode electrode to the cathode electrode, the organic light emitting diode emits light to represent colors. 
     The organic light emitting display as above has various advantages such as an excellent color representation, slimness, etc. so that it is widely used in a variety of applications, e.g., PDAs, MP3 players, display monitors, and TVs, in addition to cellular phones. 
     SUMMARY OF THE INVENTION 
     The present invention is a luminance correction system and method capable of reducing manufacturing process time by reducing time to adjust white balance. According to a first aspect of the present invention, a luminance correction system includes: a data signal application module that applies a data signal to a display region to -emit light at a maximum luminance; a luminance measurement module that measures luminance of a pixel in the display region to which the data signal is applied; a comparator that compares the measured luminance with a target value of luminance to obtain a difference value therebetween; a memory storing a lookup table that includes luminance variations of R, G, and B pixels in the display region corresponding to the difference value; a data adjustment module that adjusts the data signal depending on the stored luminance variations of the R, G, and B pixels and transfers it to the data signal applying module; a color coordinate judgment module that judges a color coordinate of the of the R, G, and B pixels; and a chroma correction module that controls chroma corresponding to the color coordinate judged by the color coordinate judgment module. 
     According to a second aspect of the present invention, a luminance correction method includes: measuring luminance of a R, a G, and a B pixel emitting light at a maximum luminance; comparing the measured luminance with a target value of luminance to calculate the difference therebetween; judging luminance variations of each R, G. and B pixel corresponding to the calculated difference value; changing luminance of the R, G. and B pixels, depending on the judged luminance variations, and correcting chroma by selecting one of a plurality of cases of color coordinate of the R, G, and B pixels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, together with the specification illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of the present invention. 
         FIG. 1  is a block diagram of an organic light emitting display according to one embodiment of the present invention; 
         FIG. 2  is a block diagram of a luminance correction system according to one embodiment of the present invention; 
         FIG. 3  is a graph showing a color coordinate; and 
         FIG. 4  is a flow chart showing an exemplary luminance correction process, according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, certain exemplary embodiments according to the present invention will be described with reference to the accompany drawings. Herein, when a first element is described as being coupled to a second element, the first element may be not only be directly coupled to the second element but may also be indirectly coupled to the second element via a third element. Further, some of the elements that are not essential to the complete understanding of the invention are omitted for clarity. Also, like reference numerals refer to like elements throughout. 
       FIG. 1  is a block diagram of an organic light emitting display according to the present invention. Referring to  FIG. 1 , the organic light emitting display according to the present invention includes a display region  100 , a data driver  110  and a scan driver  120 . 
     The display region  100  includes a plurality of pixels  101  each of which includes an organic light emitting diode (not shown) emitting light corresponding to flow of current. Also, the display region  100  is arranged with a plurality of scan lines S 1 , S 2 , . . . Sn- 1 , and Sn formed in a row direction and transferring scan signals, and a plurality of data lines D 1 , D 2 , . . . , Dm- 1 , and Dm formed in a column direction for transferring data signals. Also, the display region  100  is driven by receiving first power ELVDD and second power ELVSS from external sources. 
     The data driver  110 , which applies data signals to the display region  100 , receives RGB video data having red, blue, and green components to generate data signals. Further, the data driver  110  applies the data signals generated by being coupled to the data lines D 1 , D 2 , . . . , Dm- 1 , and Dm to the display region  100 . 
     The scan driver  120 , which applies scan signals to the display region  100 , is coupled to the scan lines S 1 , S 2 , . . . , Sn- 1 , and Sn to transfer the scan signals to a specific row of the display region  100 . The pixel  101  transferred with the scan signals is transferred with the data signals output from the data driver  110  so that driving current is generated in the pixel  101  to be flown to the organic light emitting diode. 
     When measuring luminance of a completed product, the organic light emitting display constituted as above may display images at a maximum luminance lower than a target value due to a manufacturing process deviation. If the measurement value of luminance is different from the target value thereof, the product is judged as a defect. Therefore, a defect judgment should be avoided by compensating for the luminance as much as the difference between the measurement value and the target value. At this time, if only the luminance is raised, white balance may be broken due to efficiency difference of the respective R, G, and B pixels. Therefore, in order to solve such a problem, the color coordinate should also be corrected after correcting the luminance of the organic light emitting display. 
       FIG. 2  is a block diagram of a luminance correction system according to the present invention. Referring to  FIG. 2 , the luminance correction system  200  includes a data signal application module  210 , a luminance measurement module  220 , a comparator  230 , a lookup table  24 , a data adjustment module  250 , a color coordinate judgment module  260 , and a chroma correction module  270 . 
     The data signal application module  210  transfers a data signal which enables a display region  100  of the organic light emitting display to emit light at a maximum allowable luminance, to each pixel to enable the display region  100  to emit light at a maximum allowable luminance. In other words, if a gray scale of  255  is a maximum gray allowable scale, the data signal application module  210  transfers the data signal corresponding to  255  to each pixel  101 . 
     The luminance measurement module  220  measures luminance and/or chroma of the display region  100  emitting light at a maximum luminance. If each pixel emits light at a maximum luminance, the organic light emitting display should ideally emit light in full white. 
     The comparator  230  compares a luminance value of the organic light emitting display measured in the luminance measurement module  220  with the target value of the luminance of the display region  100  to be corrected, and determines the difference between the measured luminance value and the target value. When the organic light emitting display emits light in full white (i.e., at a gray scale of 255), and the organic light emitting display is designed to have a luminance of 300 cd, the luminance target value thereof becomes 300 cd. At this time, if the measured luminance value is 270 cd, the difference judged in the comparator  230  becomes 30 cd. 
     The lookup table  24  stores luminance variations of the respective R, G, and B pixels corresponding to a difference between a measured luminance value and the target value. In other words, the lookup table  240  stores luminance variations of the respective R, G, and B pixels for a luminance change of 30 cd. The luminance change may be accomplished by controlling gamma values of the R, G, and B pixels. The luminance of the respective pixels can be numerically changed at the same time by using the luminance variations of the respective R, G, and B pixels stored in the lookup table  240 , making it possible to reduce a luminance correction time. 
     In some embodiments, the lookup table  240  may be constituted as shown in the following table 1. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 R 
                 G 
                 B 
                   
               
               
                   
                 Luminance 
                 Luminance 
                 Luminance 
                 Luminance 
               
               
                   
                 variations 
                 variations 
                 variations 
                 variations 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 +3 
                 +3 
                 +3 
                 L (+3) 
               
               
                 2 
                 +2 
                 +2 
                 +2 
                 L (+2) 
               
               
                 3 
                 +1 
                 +1 
                 +1 
                 L (+1) 
               
               
                 4 
                 0 
                 0 
                 0 
                 L (0) 
               
               
                 5 
                 −1 
                 −1 
                 −1 
                 L (−1) 
               
               
                 6 
                 −2 
                 −2 
                 −2 
                 L (−2) 
               
               
                 7 
                 −3 
                 −3 
                 −3 
                 L (−3) 
               
               
                   
               
            
           
         
       
     
     The data adjustment module  250  makes changes to the luminance of the R, G, and B pixels corresponding to the luminance variations of the R, G, and G pixels stored in the lookup table  240 . In one embodiment, the data adjustment module  250  changes the luminance by converting the gamma values. 
     The data value to which the gamma value changed by the data adjustment module  250  is applied is transferred to the data signal application module  210 . The data signal application module  210  transfers the data value is applied to the display region  100  of the organic light emitting display and thereby, allows the display region  100  to emit light corresponding to the data value to which the changed gamma value is applied. As a result, the display region  100  will have the target value of luminance. 
     The color coordinate judging module  260  judges a color coordinate of the display region  100  using the output of the luminance measurement module  220 . When the luminance of the respective R, G, and B pixels is corrected, a color coordinate thereof varies, therefore, the white balance of the pixels may also be changed. To solve such a problem, the color coordinate judgment module  260  judges the color coordinate of the organic light emitting display. 
     In some embodiments, the color coordinate judgment module  260  divides the color coordinate of the respective R, G, and B pixels into four cases (quadrants) depending on the measured white color coordinate, as shown in  FIG. 3 . In  FIG. 3 , the measured color coordinate of the display region  100  is shown to correspond to the second case. 
     The chroma correction module  270  corrects chroma according to cases judged in the color coordinate judgment module  260 . A different correction of the chroma is then applied to the pixels depending on whether the luminance is high or low. 
     Table 2 shows a case where chroma is corrected in the chroma correction module  270 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Case of high luminance 
                 Case of low luminance 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 case 
                 case 
                 case 
                 case 
                 case 
                 case 
                 case 
                 case 
               
               
                   
                 1 
                 2 
                 3 
                 4 
                 1 
                 2 
                 3 
                 4 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 R 
                 − 
                   
                   
                 − 
                   
                 + 
                 + 
                   
               
               
                 G 
                   
                 − 
                   
                   
                   
                   
                   
                 + 
               
               
                 B 
                   
                   
                 − 
                 − 
                 + 
                 + 
               
               
                   
               
            
           
         
       
     
     Therefore, in the case of  FIG. 3  (case 2), when the luminance of the display region  100  is higher than the target value thereof, the chroma correction module  270  lowers green chroma. When the luminance of the display region  100  is lower than the target value thereof, the chroma correction module  270  raises red chroma and blue chroma. Therefore, the control on the chroma is divided to and performed by a corresponding case, making it possible to reduce time to correct the chroma. 
       FIG. 4  is a flow chart showing an exemplary correcting luminance process . 
     Step  400 : A data signal is applied to the organic light emitting display to cause the display to emit light at a maximum luminance, and then the luminance of a display region of the organic light emitting display is measured. 
     Step  410 : The measured luminance and a target value of luminance are compared to determine the difference therebetween. 
     Step  420 : If the measured luminance and the target value of luminance are identical or within a predetermined range, no correction is needed and the process ends. In one embodiment, such an instance of the difference value being identical or within a predetermined range is indicated in the lookup table, as no change (i.e., end the correction process). 
     Step  430 : If the measured luminance and the preset target value of luminance are not identical or the difference is beyond a predetermined range, the luminance variations of the R, G, and B pixels are determined using the difference between the measured luminance and the target value of luminance. The luminance variations are determined using a lookup table, wherein the lookup table includes the luminance correction range of the R, G, and B pixels corresponding to the difference between the measured luminance and the target value of luminance. Also, if the difference between the measured luminance and the target value of luminance corresponds to an intermediate value of the luminance variations, higher luminance variations are selected. 
     Step  440 : The luminances of the R, G, and B pixels are changed by applying the luminance correction range of the R, G, and B pixels. The luminances of the R, G, and B pixels are controlled by correcting a gamma value. Then, the luminance and chroma are observed. 
     Step  450 : The measured values of the luminance and chroma are determined depending on the observed luminance and chroma and compared with the (preset) target value thereof. 
     Step  460 : At this time, if the target value and the measurement value are identical or their difference is within a predetermined range, the correction work is completed. 
     Step  470 : If the target value and the measurement value are not identical or their difference is beyond a predetermined range, it is determined which one of the four cases the measurement value of the chroma belongs. 
     Step  480 : The color coordinate is controlled by corresponding to the relevant case and then step  450  is performed again. 
     With the luminance correction system and method according to the present invention, picture quality can be improved by adjusting white balance and the manufacturing process time can be reduced by reducing time to adjust the white balance. 
     While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.