Patent Document

This application claims the benefit of the Korean Patent Application No. 10-2005-0056831 filed on Jun. 29, 2005, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a light emitting display device, and more particularly to a light emitting display device in which dynamic gamma values are converted and applied. 
     2. Discussion of the Related Art 
     A light emitting device used for light emitting display is a self-luminescent device in which a light emitting layer is formed between two electrodes. The light emitting device can be divided into an inorganic light emitting device and an organic light emitting device depending on the material used. The light emitting device can be further divided into a passive matrix type light emitting device and an active matrix type light emitting device. 
       FIG. 1  is a graph showing performance of a general light emitting display device in which a fixed gamma value is applied. As shown in  FIG. 1 , the general light emitting display device uses a fixed gamma value optimized for a particular test pattern situation. Accordingly, the general light emitting display device cannot suitably adapt for a multimedia display applications. Thus, when continuously displaying an image with high luminance, general light emitting device become degraded, resulting in a shortened life span. 
     In general, video images (i.e., moving pictures) require high luminance in order to display the high contrast between light and dark areas. Text-oriented images require relatively low luminance since readability is important. As a result, in the light emitting display, if unnecessarily high luminance is provided for text-oriented images with a full white background for readability, the life span of the light emitting display is shortened and its power consumption is increased. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a light emitting display device that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a light emitting display device that dynamically adjusts gamma values. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the display device comprise a pixel circuit unit comprising a plurality of pixels to display an image, a data driver to supply data signals to the pixel circuit unit, a scan driver to supply scan signals to the pixel circuit unit, a black/white transition detector to detect a degree of black/white transition of the image, a gamma corrector to adjust the data signal by providing a gamma value to the data driver, and a timing controller to apply control signals to the data driver and the scan driver, receive the degree of black/white transition from the black/white transition detector, and provide a corrected gamma control signal to the gamma corrector according to the degree of black/white transition. 
     In another aspect, the dynamic gamma control method in a display comprise receiving image data of an image to be displayed on a screen, outputting the image data onto the screen, detecting a degree of black/white transition of the image, and controlling luminance of the image output onto the screen by applying a gamma value that has been corrected according to the degree of black/white transition. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a graph showing performance of a general light emitting display in which a fixed gamma value is applied. 
         FIG. 2  is a schematic block diagram of a light emitting display device in accordance with an exemplary embodiment of the present invention. 
         FIG. 3  is a graph showing application of dynamic gamma voltages in accordance with the exemplary embodiment of  FIG. 2 . 
         FIG. 4  is a flow chart illustrating a dynamic gamma control process in accordance with an exemplary embodiment of the present invention. 
         FIG. 5  is a view showing an example of an image with a large degree of black/white transition. 
         FIG. 6  is a view showing an example of an image with a small degree of black/white transition. 
         FIG. 7  is a view showing an example of an image with a plurality of black/white transition reference values. 
     
    
    
     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. 
       FIG. 2  is a schematic block diagram of a light emitting display device in accordance with an exemplary embodiment of the present invention. As shown in  FIG. 2 , a light emitting display device  10  according to the exemplary embodiment of the present invention comprise a pixel circuit unit  12 , a data driver  14 , a scan driver  16 , a timing controller  18 , a black/white transition detector  20 , and a gamma corrector  22 . 
     The pixel circuit unit  12  comprises a plurality of light emitting diodes (LEDs)  28  where each LED defines a pixel. Each LED  28  is a self-luminescent device for illuminating a light emitting material, such as phosphor, by re-combining electrons and holes. Each LED comprise an organic light emitting layer, for example, formed at each position where data lines  24  and scan lines  26  cross. The pixel circuit unit  12  displays images on a screen via the plurality of LEDs  28 . Other types of LEDs may be used without departing from the scope of the present invention. 
     The data driver  14  applies data signals to the LEDs  28  of the pixel circuit unit  12  through the data lines  24 . A single data driver may be employed or two or more data drivers can be used without departing from the scope of the present invention. The scan driver  16  applies scan signals to select the LEDs  28  of the pixel circuit unit  12  through the scan lines  26 . A single scan driver may be employed or two or more scan drivers can be used without departing from the scope of the present invention. 
     The timing controller  18  supplies red, green, and blue (R, G, B) control signals to the data driver  14  and supplies scan control signals to the scan driver  16 . In addition, the timing controller  18  supplies gamma control signals to the gamma corrector  22  such that the gamma corrector  22  can control a gamma value to be provided to the data driver  14 . 
     The gamma control signal from the timing controller  18  can differ according to a degree of black/white transition of an image to be displayed by the pixel circuit unit  12 . In particular, the black/white transition detector  20  detects a degree of black/white transition of an image and provides a corresponding value to the timing controller  18 . 
     The gamma corrector  22  receives a gamma control signal generated by the timing controller  18  according to the degree of black/white transition provided from the black/white transition detector  20 . The gamma corrector  22  applies gamma values to the data driver  14  according to the gamma control signal. Accordingly, the data driver  14  supplies data signals each having a different luminance level to the pixel circuit unit  12  to thereby control luminance of the LEDs  28 . 
       FIG. 3  is a graph showing application of a dynamic gamma voltage in accordance with the exemplary embodiment of the present invention. As shown in  FIG. 3 , if the degree of black/white transition of the image detected by the black/white transition detector  20  is low, the gamma corrector  22  provides a gamma reference voltage or gamma value lower than a gamma reference voltage or gamma value fixed at the general light emitting display (indicated by a solid line) to the data driver  14 . On the other hand, if the degree of black/white transition of the image detected by the black/white transition detector  20  is high, the gamma corrector  22  provides a gamma reference voltage or gamma value higher than the gamma reference voltage or gamma value fixed at the general light emitting display to the data driver  14 . That is, different gamma values are applied depending on the degree of black/white transition of images. In the present invention, application of the different gamma values according to the degree of black/white transition of the image is referred to as dynamic gamma control. 
       FIG. 4  is a flow chart illustrating a dynamic gamma control process in a light emitting device display according to the exemplary embodiment of the present invention. In addition,  FIGS. 5 to 7  show various images having different degrees of black/white transitions. For instance,  FIG. 5  is a view showing an example of an image with a large degree of black/white transition, and  FIG. 6  is a view showing an example of an image with a low degree of black/white transition.  FIG. 7  is a view showing an example of an image with a plurality of black/white transition reference values. 
     As shown in  FIG. 4 , an image is applied to the pixel circuit unit  12  at step S 10 . The image displayed on the pixel circuit unit  12  may be a text image with a full white background for readability as shown on the left portion of  FIG. 5 , or a picture or video with diverse information as shown on the left portion of  FIG. 6 . 
     Next, an input image is recognized by analyzing the images in a horizontal direction at step S 11 . In particular, higher amounts of horizontal data correspond to darker images. Therefore, the degree of black/white transition can be determined and corresponding values obtained by analyzing the amount of data in the horizontal direction at each reference point. The degrees of black/white transition of a text-centric image in which text and background are repeated in horizontal direction and a general image in which various image information exist are shown on the right portions in  FIGS. 5 and 6 , respectively. 
       FIG. 7  is a view showing an example of an image with a plurality of black/white transition reference values. As shown in  FIG. 7 , the degree or number of times of black/white transitions is calculated at step S 12  according to a plurality of reference values (shown by reference lines  1 ,  2 , and  3 ) based on the obtained data values in the horizontal direction. Accordingly, the text image as shown in  FIG. 5  has a high degree of black/white transition at reference point  1  but has a low degree of black/white transition at the reference points  2  and  3 . Meanwhile, the picture or video image as shown in  FIG. 6  has a low degree of black/white transition at all the reference points  1 ,  2 , and  3 . Accordingly, by employing the three reference lines, precision of the degree of black/white transition can be increased. As a result, in cases where the degree of black/white transition is high as shown in  FIG. 5 , the image may be determined as a text image with a full white background for readability, whereas in the case where the degree of the black/white transition is low, the image may be determined as a picture or video for multimedia application and not just for readability. 
     As shown in  FIG. 4 , a gamma value is corrected according to the degree of black/white transition at step S 14 . At step S 15 , if the degree of black/white transition is large as shown in  FIG. 5 , a gamma reference voltage or a gamma value with a smaller slope as shown in  FIG. 3  is applied to the pixel circuit unit  12  to display the image. If the degree of black/white transition is low as shown in  FIG. 6 , a gamma reference voltage or a gamma value with a larger slope as shown in  FIG. 3  is applied to the pixel circuit unit  12  to display the image. In this manner, different gamma values may be applied according to the degree of black/white transition of an image displayed on the screen to suitable control luminance according to the image to be displayed. 
     In the above-described exemplary embodiment of the present invention, the display is an organic light emitting display with pixel circuit unit  12  having a plurality of LEDs  28 . However, the pixel circuit unit  12  may be directed to various display devices such as a plurality of plasma display elements, liquid crystal display elements, light emitting devices, and an inorganic light emitting device without departing from the scope of the present invention. 
     In addition, in the above-described exemplary embodiment of the present invention, the LEDs  28  may be active matrix type organic light emitting elements. However, the LEDs  28  may be passive or simple matrix type light emitting elements in which an organic light emitting layer is formed at each position where first and second electrodes cross. 
     Further, in the above-described exemplary embodiment of the present invention, the degree of black/white transition is explained as a degree of transition from black-to-white in the vertical direction with respect to the total amount of data in the horizontal direction. However, the degree of black/white transition can be also calculated by the total amount of data on the entire screen without departing from the scope of the present invention. 
     Moreover, in the above-described exemplary embodiment of the present invention, the degree of black/white transition is measured based on three reference lines. However, different number of reference lines may be used without departing from the scope of the present invention. 
     Furthermore, in the above-described exemplary embodiment of the present invention, the gamma corrector  22  is indicated as a separate unit. However, the gamma corrector  22  may be a digital gamma unit included in the data driver. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the light emitting display device of the present invention without departing form the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Technology Category: g