Grayscale Distortion Correction Method for Hysteresis Characteristics of Electrowetting Display
Electrowetting Display(EWD)not only has the advantages of ultra-low power consumption,can reading under strong light,paper-like reading experience,but also has the advantages of high response speed and video playback that Electronic Paper Displays(EPD)does not have.However,problems such as oil splitting,oil backflow,charge trapping,hysteresis effect,hinder the development of EWD.Hysteresis is an important reason for the gray distortion of EWD.Aiming at the phenomenon that the luminance displayed by the same driving voltage is different in the voltage rise stage and the voltage drop stage due to the hysteresis characteristics of EWD,this paper proposes a gray distortion correction method for the hysteresis characteristics of electrowetting display.Firstly,we designed and built a test platform.The test platform is used to measure the change of EWD aperture ratio under different voltages.The test platform consists of a microscope(with a high-speed CCD camera),a function generator,a power amplifier,and a PC.At the same time,we developed a program to measure the aperture ratio with Labview,which was run on PC.Part of the function of the program is to output test voltage.This function uses PC as the master computer and function generator as the slave computer,and uses SPCI to communicate between them.The output voltage of the function generator is amplified by the power amplifier and then applied to the EWD.The second part of the program is to detect the degree of ink shrinkage.This function uses PC as the master computer and microscope with camera as the slave computer.When the voltage is applied to the EWD,the ink begins to shrink,and the camera collects the ink status in the form of image data and sends it back to the master computer.The last part of the program is to calculate the aperture ratio with Matlab.After the image data is collected and transmitted to Matlab,the image is processed by using the program we wrote in advance in Matlab.The corresponding aperture ratio at that applied voltage will be calculated and saved.Secondly,the influence of hysteresis characteristics on the photoelectric curve was measured at different voltage range.The lowest driving voltage of EWD,above which the ink begins to shrink,and the highest driving voltage,above which the ink will cross the pixel wall,are used as the measurement boundary.The measured aperture ratio data is used as the basis for curve fitting,and quadratic polynomial is used for curve fitting.The correction methods is designed based on the obtained curves.The main correction methods are as follows:when the image data enters,it is converted to the corresponding gray scale and the aperture ratio.The initiation voltage is determined according to the changing trend of the image data According to the difference of starting voltage,select the appropriate fitting curve,calculate the corrected driving voltage,achieve the correct luminance.The judging method of the initiation voltage is as follows:when the three consecutive frames of image data have a increasing-decreasing or increasing-decreasing change,the initiation voltage is the knee-point voltage,and vice versa.Finally,we use the luminance meter to measure the luminance in the darkroom environment.The experimental results show that the actual luminance of each gray scale will be affected by the electrowetting hysteresis characteristics,and there is a significant difference between the voltage rising stage and the voltage dropping stage.The maximum relative luminance difference can reach 20.43%.After correction by the proposed correction method,the relative luminance difference of gray scale decreases from 20.07%to 0.01%,with a reduction ratio of 99.93%.The relative luminance difference decreased by 10.84%on average,and the reduction ratio was 80.98%.The highest degree of aperture ratio distortion was reduced from 5.67%to 0.13%,with the reduction ratio was 97.7%.On the other hand,using human eyes to observe the correction results,it can be found that the actual display effect after correction is significantly improved compared with that before correction.
万方数据
维普
