1. A dynamic polarity control method for driving a liquid crystal display (LCD), comprising: obtaining gray level information which indicates gray levels of dots in an image to be displayed; applying the gray level information to each of a plurality of polarity patterns to obtain a plurality of combined patterns, wherein each of the polarity patterns has an individual polarity distribution; summing up the gray levels of each of the combined patterns; and selecting a final pattern from the plurality of polarity patterns according to the summed results and at least one of a plurality of selectable selection rules, to drive the LCD for displaying the image.