DEVELOP - Adobe Photoshop Lightroom 3: Streamlining Your Digital Photography Process - page 214

Applying the local adjustment brushes
Click and drag your cursor to paint over areas of the image you want to adjust.
Using a tablet and stylus is even better.

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As you paint, a mask is applied to the image that constrains the adjustment to
the painted area. A node pin is placed at the point of the mask where you started
painting. When you're done, press Enter or Return to apply that brush, which also
makes a new adjustment brush mask.

As with graduated i lters, you can set the adjustments that are applied with the
brush masks both before and at er you create them.

Using a single mask, the adjustment can be applied in multiple spots, anywhere
in the photo. You can also create additional masks and modify or delete existing
masks. Each mask can have its own settings. Apply separate masks in dif erent
areas of the photo to apply unique adjustments in those areas.

A single mask can also have multiple brush applications using dif erent brush
settings, so some areas could be stronger than others, though I don't recommend this.
I think it's better to use single applications of the brush for very specii c settings. h is
gives you a lot more control.

Place your cursor over a node pin to temporarily show the mask overlay. To select
a brush mask, click its node pin. A solid black center indicates a brush mask node
is active; only one can be active at any given time (though none may be).

To change the values of the adjustments, click and drag let /right over the node
pin. All adjustments for that mask will be increased or decreased simultaneously,
relative to their starting values.

Hold Shift while painting
h is will constrain the brush stroke to a straight line.

With the brushes active, press Return or Enter
… to make a new brush instance.

Be economical with the number of brush masks
… but use as many as necessary for the work you need to do. Just as with global
adjustments, you should be economical with your application of localized
adjustments. For example, if you want to dodge multiple areas of the photo using
the same adjustment, use just one mask for all the areas, rather than separate
masks for each of them. At minimum, though, you will need separate brush
applications for dodging and burning.