David Pogue's Digital Photography: The Missing Manual

Backing Out, Undoing, and Restoring

Before you go to town, tweaking your photos to perfection (or into unrecognizability), it's good to know that iPhoto and Picasa are incredibly forgiving.

Undo

After any change, you can change your mind:

• iPhoto. To undo a change, choose Edit → Undo (⌘-Z). The wording changes to reflect what you've just done: Undo Crop, Undo Rotate Photo, or whatever.

  Tip

  iPhoto Tip: After making any kind of edit, it's incredibly useful to compare the "before" and "after" versions of your photo. So useful, in fact, that Apple has dedicated one whole key to that function: the Shift key on your keyboard. Hold it down to see your unenhanced "before" photo; release it to see the "after" image. By pressing and releasing Shift, you can toggle between the two versions of the photo to assess the results of the enhancement.

• Picasa. On the left-side editing panel, the lower-left button always says Undo. It might say Undo Crop, or Undo Straighten, or Undo whatever-it-is-you-just-did.

In fact, using Undo, you can back out of your changes no matter how many of them you've made. The only catch is that you must back out of the changes one at a time. In other words, if you rotate a photo, crop it, and then change its contrast, you must use the Undo command or button three times—first to undo the contrast change, then to uncrop, and finally to unrotate. (In iPhoto, you must do this Undoing while you're still in Edit mode. Picasa's Undo button, on the other hand, still works even ...