The histogram is a graph showing all the pixels in the image and their tonal range, and is very handy for highlighting problematic areas of a photograph. The left side of the graph represents the shadow or black values, the middle the midtones and the right side represents the highlights of the image or white values.

Here’s a technique that will work in any version of Photoshop. It enables you to quickly brighten up underexposed sections of the shot without burning out correctly exposed areas.