A display driving unit used in a liquid crystal display (LCD) stores two γ curves. When the LCD displays images, the display driving unit determines the luminance of the image in a first sub-period for displaying the image according to the gray level of the image and the first γ curve, and determines the luminance of the image in a second sub-period for displaying the image according to the gray level of the image and the second γ curve. The LCD displays the image in the luminance determined according to the gray level of the image and the first γ curve in the first sub-period and displays the image in the luminance determined according to the gray level of the image and the second γ curve in the second sub-period.