GND simulation, Gimp tutorial
GND filters are used to give a better exposure to the sky, and you can fake it.
GND filtersare very useful in photography and can be easily faked with Gimp. If the sky is overexposed compared to the ground (generally always) the result will look very nicer, and the realization is incredibly easy.
GND filters are a smoked glass, that is placed in front of the lens, that gradually darken the sky and avoid overexposed areas. If you shoot with a real GND filter (as in the picture below) the filter must be positioned in the right place, exactely on the horizon. With Gimp this operation is much easier, and the results are great. Real filters, such as simulated, have different degrees, one for each situation that you could find.
Simulate a GND filters with Gimp
is really easy, the first step is create a rectangular selection a
little bit over the horizon line, if you have an irregular horizon,
consider a medium point or the higher one, I suggest you to try both
options and choose your favourite.
If you are not confortable with selections you can read this tutorial.
Feather the selection, the intensity of
the feather should be about the 20-30% of the height in pixel of the
image (you can read the value of the ruler on the left of the image, or
open Image - Scale Image, and read the height value).
Open Select - Feather and set the right value.
Now press Ctrl+C, then Ctrl+V. A new Floating selection will appear in the Levels Window,
Right Click on it and select New Level.
Another way to get the same result is click Edit - Copy, and then Edit - Paste As - New Layer.
Set Multilply as blend mode, leave the opacity to 100%, then Right Click on the
Pasted Layer - Merge Down.
If you prefer a lighter effect, you can change the opacity value with a smaller one, if you prefer an heavier effect you can paste again the floating selection and redo this step
As I promised you, simulate GND Filters with Gimp is really easy to do, and the results are great.
Another way to get a similar result is the exposure blending, if you are interested read this tutorial.