Create a selection around a selection border

The Border command lets you select a width of pixels inside and outside an existing selection border. This can be useful when you need to select a border or band of pixels around an image area, rather than the area itself, for example to clean up a halo effect around a pasted object.

Original selection (left), and after Border command: 5 pixels (right)

Use a selection tool to make a selection.
Choose Select > Modify > Border.
Enter a value between 1 and 200 pixels for the border width of the new selection, and click OK.
The new selection frames the original selected area, and is centered on the original selection border. For example, a border width of 20 pixels creates a new, soft-edged selection that extends 10 pixels inside the original selection border and 10 pixels outside it.