MacDevCenter.com: The Missing Digital Photography Hacks - Interpreting camera histograms

MacDevCenter.com: The Missing Digital Photography Hacks

A good exposure will typically display information across the entire width of the graph. Shadow information is on the left side, highlights are on the right, and midtones are, well, in the middle. The particular shape of the graph depends on how the light is distributed throughout the picture.

What you want to be leery of is when the graph information bunches up on one side or another. A graph heavy to the left usually indicates underexposure with the image appearing dark (move exposure compensation to 1). If everything is scooted over to the right, that often indicates overexposure with blown highlights and washed out shadows and midtones (move exposure compensation to -1).

As you become experienced working with the histogram, you'll begin to correlate spikes in the graph with various intense tones in the actual picture. And when you open your shots in your favorite image editor, such as Photoshop Elements, you can adjust the photo's tones using the histogram display in the Levels dialog box (Enhance > Adjust Brightness/Contrast > Levels). Think of it as another way to look at your pictures.