| Originally posted by Leerod |
Vary your feather on the tool along with the transparency. Hair should have a high feather and transparency. Distinct edges need a very low feather and transparency.
Leerod, I think that this is referring to is the options available on both the lasso tool (for selections) or the paintbrush tool (for masking). The lasso tool allows you to set a feather distance (in pixels.) The paintbrush tool allows you to pick a brush with hard or soft edges (the softer the edge the more "feathered" the selection/mask) and also set an opacity of the brush (a lower opacity softens the brush even more).
In Chapter 2 of the Photoshop Retouching Handbook by Carol Braverman, she goes into detail about examining an image to determine which edges are "hard" and which edges are "soft". For example, the edges of a vase might be sharp (hard), but the shadow it casts might be soft. If you want to select both the vase and the shadow, you probably want to use a larger feathering/softer brush on the shadow than on the vase.
In the example quoted above, the hair does not create as sharp an edge with the background as does an arm, for example. Of course, you have to be careful that you don't feather around the hair too much - esp. if you're extracting a person to a different colored background, otherwise, you bring some of the original background along with the person.
Does that make any more sense, or did I just complicate things?