Page 124 - Photoshop for Lightroom Users – Scott Kelby 2nd Edition

Step Four:
The secret to selecting hair is to use the Refine Edge Brush tool (R; the second tool down in the Toolbar on the left side of the workspace). All you have to
do is take the brush, let its edge extend over the areas you want to select (as shown here, where about 1/3 of it extends onto her hair), and paint along those
parts of her hair. To change the size of the brush, use the Left/Right Bracket keys to make it smaller/larger. For those fan-blown wisps of hair, just paint
over them too—as you paint over them, you’ll see the red tint go away, and those areas turn to full color (as seen here). Look at those areas in the previous
step—they had a red tint over them (and you could see parts of the gray background), but now it’s gone because they are now part of our selection. Don’t
paint too quickly—there is some serious math going on in the background, and you might even see a small circular “wait” cursor appear for a moment
while it’s working its magic.