Most of the time, your digital camera errs on the side of caution and serves up an image that is too bright. Sometimes the camera does just the opposite and gives you an image that is darker than the scene before you. When this occurs, here are three things you can try that may alleviate the problem:
Use exposure compensation to increase the exposure. Increasing the exposure will brighten the image, but may blow out some highlights to pure white. However, this is the route to go if there is important information in the dark areas of the scene.
Lock exposure on the part of the scene that is the most important. Check your camera manual to see if locking exposure is an option for your camera. On many cameras, move the center auto-focus point over the area of the image that is the most important, and then press a button to lock the exposure at that point of the image. Note that this may adversely affect the exposure for other parts of the image.
Move to a slightly different vantage point. When an image is too dark, the camera is compensating for a very bright object that takes up a large portion of the frame. For example, if you’re photographing a scene late in the afternoon and a large part of the scene is bright sky, the camera will choose settings to properly expose the sky. If the sky is the most important part of the image, the camera is making the right choices. If the sky is not the most important part of the image, move to a different vantage point or recompose the image so that the sky is not the predominant part of the image.