Estimation Method of Optimized Overdriving Values for a TN mode LCD Panel

Abstract

Liquid Crystal Displays (LCDs) are subjected to motion blur which is caused by slow LC response time and hold driving method of active matrix display. To improve the motion quality of LCDs, many technologies such as double frame rate with black data insertion, scanning backlight have been proposed to simulate impulsive driving. Overdrive method is one of the technologies to reduce the LC response time, resulting in a reduction of motion blur. These days, the overdrive technologies have been expanded to TN mode LCD panels such as note PC applications. Based on the dynamic compensation methods, the overdrive gray level could be determined by adjusting the overshooting gray level at the gray to gray transition. But it is complicated and time consuming to generate overdrive values in look-up table because the overdrive values depends on several factors such as gamma curve, response time, human visual recognition, and LC characteristics. When the overdrive level is over-tuned, the edge of moving pattern shows different luminance level. This side effect perceived by human eyes degrades the moving image quality. There have been several proposed methods to find optimal overdrive levels. Those methods which are based on LC response curve do not reflect human visual system. Even in the case of method that considers human visual system, the obtained overdrive value has the possibility to be overdosed, so the previous methods cannot be guarantee to prevent double edge problem in the moving image. In this thesis, we have carried out the experiment about three types of TN mode 15.4-inch WXGA panels with different on-off response time, gamma curve at 60Hz driving scheme. In order to find the optimized overdrive value, we adjust the overdrive level manually for each gray to gray transition until the optimal overdrive value is obtained. When the test pattern is scrolled, the observers might see brightened or darkened double edge at the moving edge of the scroll pattern if the overdrive level is overdosed. The optimal overdrive level is obtained, and the look-up table is made for each three different type of TN mode panel. Based on the result of experiment and analysis, we produced the algorithm to gain the optimal overdrive values, and verified the algorithm by applying the calculated optimal value to the loop-up table.