There is more to creating a Quickmask than simply painting an area and converting it to a selection. Remember that Photoshop lets you use all of its tools on the painted mask you've created. This means that you can apply local or global sharpen/blur effects, further modifying the selection you've created. Once you have a basic Quickmask area defined, you can use the following methods to further modify the mask:
The Sharpen/Blur/Smudge tool is an effective way to modify local edge areas
of a selection. For example, if you want to have the edge of a selection fade
out on one side, but be crisp and sharp on the other, you would use the Sharpen
and Blur tools as needed. In the same way, selecting the smudge tool lets
you smear and distort selection edges in varying degrees(Figure 18.5).
The key differentiator between these approaches and selecting feather edges
or a distort filter, for example, is that these commands apply their effects globally to the entire selection, while the Sharpen/Blur/Smudge tools allow you to modify local areas of the mask. Quickmask allows you to use individual tools on specific areas of a selection as needed.
The Dodge/Burn tool provides another way to modify a mask by making
the mask value darker or lighter. This approach allows you to darken
an edge, which sharpens it and eliminates any anti-aliased or feather
effects that may be applied there. Conversely, the Dodge tool lets you
soften an edge, creating more of a feathered selection. In this respect,
the dodge/burn tool modifies a mask in the way as the sharpen/blur tools,
but it does go one step further.
The Dodge/Burn tools also let you modify the translucency of a mask, making it more opaque or transparent. You can use the burn tool to darken and solidify a selection area, while the Dodge tool lightens and feathers an area. This lets you move beyond modifying only the edges, letting you modify internal areas of a mask and selection as well(Figure 18.6).
Once you've started a translucent mask, either with a gradient, or
any of the tool listed above, you can modify the relative translucency
Its as simple as selecting Image>Adjust>Curves while in Quickmask mode, and moving the curve up or down to lighten or darken the current mask. You can make similar modifications with the Brightness /Contrast controls, or the Levels controls.
It is also possible to modify a mask using the four edge effects controls found at the bottom of the Adjust Submenu in the Image menu. These controls can deliver quick shortcuts to various mask editing requirements.