To improve contrast ratio of the image on a backlit display plane such as a liquid crystal display (“LCD”), each area of the image that has separately controllable backlight may be given full backlight until an average or composite brightness of the image in that area is less than a threshold value at which light leakage through the image from full-strength backlight begins to be noticable by a viewer. For image areas with composite brightness less than that threshold, backlight brightness may be reduced in proportion to how much below the threshold the area's composite image brightness is. Backlight brightness may also be adjusted for other image aspects such as (1) the presence of bright pixels in an otherwise relatively dark area, (2) whether the area is adjacent to one or more other areas in which the image information is in motion, and/or (3) time-averaging of image information over several successive frames of such information.