Take a look at this photo of Metlako Falls in the Columbia River Gorge. Besides the vibrant colors, you will notice that every part of the photograph seems to be correctly exposed. A histogram can help us determine whether a photo is properly exposed, and if the photo needs to be bracketed in order to capture the entire dynamic range of the scene. Sometimes, we process a single image multiple times in order to get proper exposure in different parts of the photograph.
Lets take a look at this scene as an example. If you wanted to expose this scene for the highlights, I would look at the bright water in the falls, and adjust the shutter speed and exposure until my histogram showed that I had captured detail in the bright areas of the image. We can do the same during post-processing… as seen in the image below.
In post-processing, I kept an eye on the highlights and histogram. I adjusted the image so that I had the detail and contrast that I wanted in the highlight. Of course, this meant that the rest of the image was drastically underexposed. I can blend the image exposed for the highlights with one exposed for the shadows and mid-tone, and the result will be a natural-looking scene with nice details throughout the image.