iPhoto ’11: The Macintosh iLife Guide to using iPhoto with OS X Lion and iCloud

Adjusting Exposure and Levels

The Adjust pane gives you control over many aspects of a photo’s appearance, but chances are you’ll use its exposure controls most often. For improving a photo’s exposure and contrast, use the Levels sliders and the Exposure slider. By adjusting them—while keeping a close eye on the photo’s histogram—you can often make dramatic improvements in a photo’s appearance.

Which tools should you use? It depends on the photo. Some photos respond better to the Exposure slider, while others benefit from levels adjustments. Still other photos benefit from both approaches: do some initial tweaks with the Exposure slider, then fine-tune the levels.

When you drag these sliders, you tell iPhoto to stretch the photo’s existing tonal ...