Special Effects - The Photoshop: Professional Retouching and Compositing Tips, Tricks, and Techniques - page 226

Figure 4.20
Note
When you're defining (creating) a brush, Photoshop makes the darkest areas
opaque and the gray areas semitransparent. White areas are completely ignored.
8. Choose Edit > Define Brush Preset, name the brush Debris , and click OK. Choose
the Brush tool (B), and in the options at the top of the screen click to open the
Brush Preset Picker. The brush we just created will appear as the very last in the
list. Click this new brush to select it, click the gear icon in the top right of the
Brush Preset Picker properties to open a menu ( Figure 4.21 ) , and choose Save
Brushes.