You can modify your pixel selection by enlarging or shrinking it, applying a feather to its edge, and/or by smoothing its curve. These options are available from the Select menu as Grow/Shrink, Feather, and Smooth, respectively.
The following settings can be adjusted from the relevant dialogs:
- Radius—controls the extent of the effect.
- Negative values for Grow/Shrink will shrink the selection while positive values enlarge it.
- Circular—if this option is unchecked (default), resizing honors the original selection shape. When checked, the selection shape is made more rounded with increasing Radius values.