If you’ve read my earlier article on using Adjustment Layers to adjust light and shade, you’ll know of my preference for non-destructive editing. So why would I recommend the always-destructive Dodge and Burn tools? Simple: they’re the best tools for tweaking a mask.
There are many, many ways to create a basic selection and to turn it into a mask, and exploring them in detail is beyond the scope of this tutorial. We’ll tackle it just one way.
Open an image with a relatively even, obviously defined background. Here, I’ve used a photo of me in the Craters of the Moon National Monument and Preserve, in Idaho. Option-Double-click the Background layer in the Layers panel to promote it to a regular “Layer 0”. This is necessary because you can’t apply a layer mask to a Background layer.
We’ll select the image background using the undersung Color Range. Choose Select > Color Range. In the dialog that appears, click on the background, then Shift-click, as you would with the Magic Wand, to extend the selection. Adjust the Fuzziness slider until the background is white and the foreground is black, then press OK.
We’ve selected the background, though we really want the foreground. Therefore, choose Select > Select Inverse (or press Command-Shift-I).
Optionally, you could choose Select > Refine Edge. This powerful tool is very useful for cleaning up a selection, but it can cause problems too. Feather is effectively a blur, and too much smoothness will destroy fine details. For a simple outline it’s great, but use with caution.
Note that Photoshop CS5’s Refine Edge introduced valuable new options, so follow the steps corresponding to your version:
In the Layers panel, you should now see your layer selected, with the layer mask next to your original layer. To really see what’s going on, we’ll now view the mask alone as a grayscale image.
Choose the Channels panel, then click on the space to the left of “Layer 0 copy Mask” to show it. Now, click on the eye in the space next to “RGB” to hide the normal layer. Click on the layer mask’s name to make sure it’s selected for editing. Depending on your image, you will probably see some noise around the edges of the selection. Ideally, we want clean white and black, with a smooth change between, and that’s what the Dodge and Burn tools can help us with.
Masks often need selective painting to be just right, but using the Brush Tool isn’t ideal. By painting, we’re ignoring the image itself, and potentially going over the edges. Can’t we paint in a way that respects the original image data? Yes.
Choose the Dodge tool (a magnifying glass lookalike grouped with a hand and a sponge). In the Options panel, choose Highlights instead of Midtones.
Now, choose the Burn tool (a hand). In the Options panel, choose Shadows instead of Midtones.
These settings will stick, and they mean that the Dodge tool can paint light grey areas to white without affecting darker tones, and the Burn tool can paint dark grey areas to black without affecting lighter tones. Read that again if it didn’t sink in.
Use the Dodge tool to paint over lighter areas to turn them white, and use the Burn tool on darker areas to turn them black. Paint straight over the edges if needed — you don’t need to be too careful. Try to use long paint strokes, as repeated work on the edges will make them too sharp and harsh.
Note that you may still need to paint with Brush tool in some areas, if they are too light or dark for the Dodge or Burn tools to be effective. Still, Dodge and Burn can be a huge time-saver when used in this way. Enjoy!