采用动态背光改善LCDs运动模糊的频域研究

Frequency Domain Study for Motion Blur Improvement on LCDs Dynamic Backlight

基于运动图像视觉感知模型和实测LCDs时间响应特性,运用调制传递函数(MTF)理论,从频域的角度讨论了采用动态背光的方法改善LCDs运动模糊的有效性。模拟分析了背光闪烁情况下背光闪烁参数与LCDs显示运动图像时的MTF(f)特性的关系及其对LCDs运动图像质量的影响。特别针对LCD所显示图像的运动特征,定义了反映MTF与速度之间关系的MTF(v)作为评价指标之一,以便更清楚地描述LCDs运动模糊与图像运动速度之间的关系。结果表明,LCDs显示运动图像时的MTF(f)具有呈辛格函数分布的低通特性,反映运动图像细节的MTF(f)高频分量随图像运动速度的增大而减小,从而导致图像清晰度下降。在背光闪烁模式中,适当选取背光闪烁的闪烁参数,如一帧内的闪烁周期数、一个闪烁周期内发光占空比、一个闪烁周期内发光时段等,可增大MTF(f)曲线的带宽、高频分量或曲线下面积,从而减小运动图像模糊程度,增加运动图像清晰度。为反映运动模糊程度与图像运动速度的关系而定义的MTF(v)曲线亦具有相同的特性。

Based on the model of Human visual system, the temporal step response curve measured from a LCD, and the theory of modulation transfer function, the validation of dynamic backlight method for improving LCDs motion blur was discussed from the view of frequency domain. The relations between the backlight blinking parameters and dynamic MTF characteristics of LCDs were simulated and analyzed at the certain moving speed. MTF（v） was specially defined as one of the index for perceived image quality assessment to reflect the relation between MTF characteristics and the image moving velocity. The results indicated that dynamic MTF（f） of LCDs has a low pass characteristics presented by Sinc function formula,and the value of dynamic MTF at high frequency components decreascs with the increase of the image moving velocity, so that the resolution of the image displayed on LCDs is degraded. The proper choice of the blinking parameters, such as cycle numbers per frame, duty cycle and temporal period in a blinking cycle, were discussed, in order to increase the bandwidth, the MTF at high frequency components or the area of the MTF（f） curve to decrease of motion blur and improve the image resolution. The MTF（v） curve specially defined for denoting the relationship between motion blur and image velocity has the same characteristics.