Even if you take a good light meter reading and set your shutter speed/aperture correctly, it is still possible to have a underexposed/dark photograph due to an inaccurate light meter. Next to taking a meter reading off of an incorrect point in your composition, an inaccurate light meter is a major cause of dark images. This is especially easy to see in point and shoot and digital cameras. With film cameras, the lab was often able to correct exposure problems when they developed film and the photographer never saw the problem. Now, we are our own photo labs, and we see the problem!
If you are using a basic point and shoot camera and it is under warranty, get it repaired as there really isn't a good workaround for you on this problem. You will either have to get the meter repaired, purchase a new camera, or continue to try to lighten the image in a digital darkroom program. Even using flash probably will not eliminate the problem as the light meter will adjust to the flash.
If your camera has a manual setting you can easily work around an inaccurate meter. You will need to take some test images to see just how badly inaccurate your meter is. Take several shots of the same subject, adjusting your aperture each time. When you view your images, note what exposure compensation produces the desired image. Note this amount and remember to "overexpose" (at least according to your light meter) your images by that amount each time.
Preventing Dark (underexposed) Photos
From Liz Masoner, former About.com Guide
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