1. A method for enhancing contrast of an image displayed on a display device comprising: receiving the image; selecting a transfer curve according to a luminance histogram of the image; enhancing the contrast of the image to produce an output image according to the transfer curve by, (a) increasing luminance levels for high-luminance pixels without substantially changing luminance levels for mid- and low-luminance pixels in the image only when the image comprises mostly low-luminance pixels; (b) decreasing luminance levels for low-luminance pixels without substantially changing luminance levels for mid- and high-luminance pixels in the image only when the image comprises mostly high-luminance pixels; and (c) increasing luminance levels for high-luminance pixels and decreases luminance levels for low-luminance pixels in the image without substantially changing luminance levels for mid-luminance pixels only when the image comprises mostly mid-luminance pixels; and displaying the output image on the display device.