82 Perfecting Your Pictures Understanding a Histogram Before you begin making advanced adjustments to your photos, you must get familiar with a histogram because it's an important part of precision photo editing. A histogram is a graph that shows how much of your photo is in the dark range (shadows), the light range (highlights), and the middle range (midtones) of brightness. Let's look at some real histograms to see how they work. 1 Click the Full Screen button photo more clearly. . You'll use full-screen view because you can see the 2 In the Source list, select Events, and double-click "Greg and Caren's Wedding." You'll find several perfect wedding photos here that you don't need to edit. The images you'll want to edit are flagged to make it easier to locate them. 3 4 Select the first photo in the Event. Click the Edit button the photo. and then click the Adjust tab. Examine the histogram and