When moving images are displayed on matrix displays which reproduce gray levels utilizing pulse-number/width-modulation techniques, degradation of the gray levels and colors are often observed. The degradation originates from a temporal non-uniformity of the light-emission pattern, which is transformed into a spatial non-uniformity of the light emission due to an after-image effect of the eyes, which follow the image motion. The degradation becomes appreciable when the product of the speed of the viewing point on a screen and the light-emission period of a pixel is greater than the pixel pitch. The degree of degradation is also affected by the pixel arrangement; disturbances for the stripe arrangement are worse than those for the triangle arrangement. The temporal uniformity is degraded when the major light-emitting blocks of the pulse-number/width-modulation change. The uniformity can be improved by dividing the blocks of the major bits. It was analytically verified that the perceived luminance of periodic light emission is proportional to the emission duty factor (which coincides with Talbot-Plateau's law) and also to the integral of f(t)dt from zero to infinity, independent of decay shape, f(t), of the after-image.