The paper proposes a global backlight dimming algorithm for CR enhancement and power reduction. S-shaped function is involved to help improve CR. Both the backlight dimming level and the turning point grayscale of the s-shaped curve are determined by the histogram of the input image. The pixels with the grayscales more than the turning point are compensated to become brighter and the pixels less than turning point become darker. The simulation results show that the proposed dimming algorithm can improve CR by average 34.95% and reduce power consumption by 11.30%.