David Pogue's Digital Photography: The Missing Manual

Fine-Tuning Exposure

The best time to adjust the exposure (brightness) of a photo is when you take it. But software can sometimes help after the fact.

Both iPhoto and Picasa have an Exposure slider:

• iPhoto. Open a photo for editing. Click the Adjust button on the toolbar (or press the letter A key) to make the Adjust panel appear. Drag the Exposure slider to adjust the overall brightness of the photo.

  Note

  iPhoto Note: iPhoto's Levels controls offer a more accurate, more nuanced way to adjust the exposure. See Juicy Bonus Features.

• Picasa. Open a photo for editing. On the Basic Fixes tab, drag the Fill Light slider to make the photo brighter or darker overall. (This same slider also appears on the Tuning tab.)

When you're editing JPEG graphics (that is, most photos from most cameras), the Exposure slider primarily affects the middle tones of a photo (as opposed to the brightest highlights and darkest shadows). If you're used to advanced programs like Photoshop, you may recognize this effect as a relative of Photoshop's gamma controls. (Gamma refers to the middle tones in a picture.)

When you're working with RAW files, however (RAW or JPEG?), this slider is even more interesting. It actually changes the way the program interprets the dark and light information that your camera recorded when it took the picture. A photographer might say that it's like changing the ISO setting before snapping ...