Have you ever had a look at the histogram on your camera’s LCD and wondered what it means? The histogram is a graphical representation of the tonal range of your photo and helps you evaluate the exposure. It’s simple to read: the blacks (0% brightness) are on the left, the whites (100% brightness) are on the right, and all the mid-tones are in between.
Watch out for histograms with dramatic spikes to the extreme ends of either side of the spectrum – which indicates that you have a lot of pixels that are either pure black or pure white. While this might be the effect you want, remember that those sections of the image probably have very little detail – and could be a hint that your image is either under- or over-exposed.