Remember the last time you gave your walls a fresh coat of paint? You probably used a roll of blue or beige masking tape to cover the baseboards and windows so you wouldn't get paint on them. Masking tape's digital equivalent--called a layer mask--is a timesaving feature in Adobe Photoshop, Photoshop Elements (version 9+), and the affordable yet powerful Pixelmator. Here's a quick primer on how to use this great tool in your digital image editing program of choice.
