1. An automatic exposure method comprising: underexposing an image of a scene by a predetermined amount during a preview mode which precedes an image capture mode for the scene; inputting underexposed image pixel data collected during the preview mode to an image processing pipeline; processing the underexposed image pixel data to obtain histogram information from the image pixel data; examining the histogram information to determine a high limit of a dynamic range for the scene; and adjusting an exposure parameter for the scene during an image capture mode based on the determined high limit.