Exposure Blending Gimp tutorial
Exposure blending allows you to correct a photo with too much contrast.
Exposure Blending is a post production method that is used used to get a better exposure and dynamic range without using hdr tecnique. This is a Gimp tutorial. Exposure blending uses two photos with two different exposure, that are blended in order to get a single photo with a perfect illumination.
The classic situation is a subject properly exposed, and an overexposed background.
This technique can be done only with two identical shots, so you need tripod (or any solid support) and a static subjects.
Another option is a single raw file with two different Raw development, but this method will generate more noise. For this tutorial I used a photo shooted during a sunset in "Passo Giau", a mountain pass in North East of Italy, the subject are the amazing Dolomites.
Set the bracketing on your camera, this option should be available in almost all cameras, you can even set manually three different exposures: -1 f/stop, 0 f/stop and +1 f/stop. Only two images will be used (0 and -1), but is a good idea to have an overexposed photo for adjust a possible too dark area.
Open Gimp and select only the sky with your favourite tool. The result should look like the image below, in red the non selected area. I used Fuzzy Select Tool. If you want to know more about selections, read this tutorial.
Feather the selection, click Selection - Feather and set 3/5 pixels of radius. Copy the sky of the first image into the second one (Ctrl+C followed by Ctrl+V, or Edit - Copy followed by Edit - Paste as - New Layer)
If the photos were shooted correctly the pasted layer will perfectly fit into the new image. If the sky is too dark, modify the levels (Colors - Levels) until the exposure is right. In this example this was unnecessary.
The image chosen for this tutorial
could induce in error. If you think that darken the sky would give the
same result you are in error, imagine if there were clouds illuminated
by direct sunlight, clouds would have been overexposed.
Another example can be a night photo with the moon, in this case exposure blending is the only way to get the stars without an overexposed moon.
There is also another effect that gives similar results in an easier way, is called GND Filters Simulation.