A graduated neutral density filter (GND) is a filter used for cameras to darken an area of the shot that is significantly brighter than the rest of the shot. like a picture of a dark forest and the bright sky, or a bright snow field and darker mountain. This howto shows you howto emulate the use of this filter on your digital photo. With a good graphics editor like Gimp you can balance the bright and dark portions of your picture without it being obvious that you modified it.