Of all the tools in the last few versions of Photoshop, the Dodge and Burn tools seem to be among the least used, possibly since digital photography has reduced the need for them. But once in a while, especially in restoring scanned-in prints, one might still try them out.
Dodging and burning, in photography, are lightening and darkening parts of an image that show some detail but not quite enough; if dark parts can be lightened a little, or vice versa, visible detail might be improved.
Once we have a decent scan, we can decide which parts are a little too dark or light. We can then select an area to work on—the key is to feather the selection by a fairly high number of pixels, how many depending on the image. That is, to make the selection fuzzy-edged, so the dodge and burn we do won’t stop too sharply at the edge and give itself away.
We then select the tool—they work pretty much the same other than which thing they do—and adjust the options. For dodging, select Shadows; for burning, select Highlights. With dodge and burn work, one can use Midtones for both, but the thinking is to affect the more “extreme” areas of the image, so experiment if needed. The Exposure control is for how much “oomph” the tool will have, or how much it will affect the area quickly. We want this fairly low, usually no more than 20-25% or so, since we want to work slowly up to the degree of effect we want. Using the Airbrush option to build up is okay to try; I find I don’t use it much, but some people have told me it’s good when you get used to it.
The real trick, at least from my experience, is that “tapping” the mouse button to apply short bursts of effect seems to be one good approach in both dodge and burn. Though we can use Undo or the History panel to go back if we overdo it, one doesn’t want to have to do it too often.
And if the effect is not very obvious, that’s because it’s not supposed to be. Remember, the goal in many cases is to have the image look as if nothing was done to it at all—as someone once wrote, “the art of concealing art.”