Digital Focus: Scale Pictures for Framing

Q&A: Judging Pictures Via the Histogram

A friend of mine says that after talking a picture, he simply looks at the histogram on the back of the camera to determine whether a picture is a keeper or not. He deletes those that are not up to standard without even looking at the image itself. Can the histogram alone be a good judge of image quality? What's your take on this practice?

--Bruce Switalla, Corpus Christi, Texas

The histogram is indeed a great little tool, Bruce. Bruce. But a histogram alone can't determine picture quality; that requires human judgment.

The histogram is a graph that displays the distribution of light and dark pixels in a photo. Many digital cameras let you view the histogram on the LCD viewfinder after snapping a picture. If yours doesn't, don't despair: Most image editing programs offer a histogram as well.

When you look at the histogram, check the pixel arrangement from left to right. If the graph is skewed too far to one side or the other, it's an indication that your picture is over- or underexposed. But there's more to it than that. Your picture may be intentionally bright or dark. And there are other factors to consider, like the composition and the mood of your photo. Sure, the histogram is great. But I'd never put so much stock in that little graph that I'd discard photos without even looking at them.

The histogram isn't always just a static display, either. Programs like Paint Shop Pro and Photoshop Elements let you use the histogram as a guide for redistributing the brightness and contrast in an image, which can dramatically improve a photo. Next week I'll show you how it's done.