Adjust a backlight of a display device according to image loading and edge statistics of an input image. When the input image is a dark scene and includes relatively more edges, a luminance of the backlight would be controlled according to the image loading of the input image and compensated the backlight for showing details of the input image clearly. When the input image is a dark scene with negligible edges, the luminance of the backlight would be controlled by image loading with no or few compensation for lowering the power consumption. When the input image is a bright scene, or when the input image includes no edge or only negligible edges, minimum compensation is applied to the backlight for lowering the power consumption.