Adding a Perfectly Square or Circular Selection in Photoshop

To add a perfectly square or round selection to an existing selection, follow these steps:

1. Press Shift and drag with the Rectangular or Elliptical Marquee tool.
Your selection is unconstrained.
2. As you drag, keeping your mouse button pressed down, release the Shift key for just a moment, and then press it down again.
Your unconstrained selection suddenly snaps into a constrained square or circle.
3. Release the mouse button before you release the Shift key.
If you don’t release the mouse button before you release the Shift key, the selection shape will revert back to its unconstrained form.

Deleting from an existing selection while drawing from the center out

To delete part of a selection while drawing from the center out, follow these steps:

1. Press Alt (Option on the Mac) and drag with the Rectangular or Elliptical Marquee tool.
2. As you drag, keeping your mouse button pressed down, release the Alt (Option on the Mac) key for just a moment, and then press it down again.
You are now drawing from the center outward.
3. Release the mouse button before you release the Alt (Option on the Mac) key.

Use this technique when you’re selecting a doughnut, tire, inflatable swim ring, and other circular items with holes in the middle.