[Paper] Mechanism of Degradation of Moving Image Quality with Pulse Width Modulation Grayscale Expression Methods

Abstract

In the display device employing the pulse width modulation (PWM) method for expressing grayscale, visual artifacts such as distortion, ghost, and color breakup appear when an image moves and observer's eye tracks the image. This paper clarifies a mechanism of moving image degradation with various PWM methods. With the PWM, the distribution of light emission within a display field time vary according to the gray levels. The variation of temporal center of light emission is transformed into spatial shift of image. When there are two non-overlapping period in the temporal light emission pattern of adjacent objects, ghost appears. The difference in the temporal distribution of light emission of color sub-pixels causes color breakup. Shape distortion and color breakup severely degrade the moving image quality when the standard left-aligned PWM is employed. The center-aligned PWM generates unacceptable ghosting. Pulse frequency modulation produces the same image quality as the pulse amplitude modulation.