To gain creative control of exposure, you can use exposure compensation, also known as exposure value (EV). This allows you to increase or decrease the exposure from what the autoexposure setting typically delivers.
If your pictures are coming out too dark (underexposed) or too light (over-exposed) and you are taking a series of pictures in the same lighting, then adjust the exposure up or down to compensate. You should never assume that you can take pictures with the wrong exposure and fix them later with software because you may not be able to.
The settings are different from camera to camera, but usually they appear as +2, +1, -1, and -2, with zero representing the default autoexposure setting. To obtain a brighter image — for example, in a backlit situation — you “dial up” using a positive value to increase the exposure. For a darker image, choose a negative value, thereby decreasing exposure. Exposure compensation lets you choose the exposure that is most likely to produce the results you're seeking.
It takes a lot of practice to get to the point where you know when to lighten or darken a scene. One feature of a digital camera that makes it easier: the LCD screen. Because it lets you preview your shot, you don't have to guess whether or not the exposure needs adjusting.
One way to avoid a poorly exposed image is to use a trick that professional photographers often employ. It's called bracketing. The bracketing process means that you take three shots: one at the recommended exposure setting, a second shot that's lighter, and a third shot that's darker, thereby bracketing the recommended exposure with two additional shots. By taking a series of shots at different exposures, you're far more likely to obtain one that's to your liking.
This shot of a ship was underexposed.
This shot of the ship was overexposed.
Exposure compensation control lets you correct exposure. Here are some typical settings and how they are used:
+2: Used when there is high contrast between light and dark areas in a scene
+1: Used with side-lit or backlit scenes, such as snow scenes, beach scenes, sunsets
0: Great for evenly lit scenes
-1: Good for scenes where the background is darker than the objects in front of it, such as when an individual is standing in front of a brick wall
-2: Used when the background is very dark and takes up a large portion of the image, and you are striving to maintain detail in the brighter areas of the scene