In order to overcome the shortcoming of previous S-shaped curve global dimming algorithm for face image, an improved S-shaped curve global dimming algorithm is proposed. The images containing faces are first figured out based on several format kinds of signals. The S-shaped curve is then established to compensate the LC pixels. Simulation results show that the improved algorithm can detect face image accurately and increase the displayed image quality effectively. Prototype testing results show that the image quality of LCD TV has improved significantly and the average display energy consumption decreases by 21.28%.