What is a "histogram"?

What is a "histogram"?

Mark Comon (Vice President, Paul's Photo, Torrance, CA) gives expert video advice on: What are some helpful features my digital camera could have?; What are features of some digital cameras that I don't need?; What is the difference between an "optical zoom" and "digital zoom"? and more...

The histogram is a graphic display of the exposure, generally displayed in the playback mode of most SLRs. General in the preview mode of some of the compact cameras. It's this funky-looking graph that you see that shows the exposure. Now, in the camera, I find the histogram to be of moderate importance. In Photoshop later on, when we're editing our pictures, the histogram is huge. You have to live and die by the histogram. What you need to know about the histogram is an ideal histogram is a bell-shaped curve. You'll never see that in real life. When you take pictures, what you want to make sure on the histogram is that there's very little touching either edge. The left edge of the histogram is your black areas. The right edge of the histogram is your white areas. You want to keep the image in the middle and not touching either edge. How do you adjust the histogram? By adjusting exposure compensation, or "plus-minus" exposure. That's how you'll shift the histogram left or right on the scale.