1. A method for improving an image quality of a liquid crystal display (LCD) device, a panel of the LCD device having a plurality of display elements each switching between a positive polarity and a negative polarity, the method comprising: receiving an input image comprising a plurality of input image sub-pixels corresponding to a plurality of display elements; generating a plurality of consecutive pictures of a predefined period number according to the input image, wherein a gray level of the input image is greater than a gray level of the plurality of consecutive pictures; setting a number of pixels required for adding a value among the plurality of consecutive pictures for every display element according to a least significant bits (LSB) of a pixel of the input image; and enforcing the number of add-value pixels of a positive polarity to be close to the number of add-value pixels of a negative polarity according to the number of add-value pixels in each of the plurality of consecutive pictures and the polarity of the corresponding display element.