How to Apply the Grow and Similar Commands in Photoshop CS6
In Adobe Photoshop CS6, the Grow and the Similar commands are close cousins to the Magic Wand tool, and to a lesser extent, the Quick Selection tool. If you’re familiar with the modus operandi of the Magic Wand tool, you know that you rarely get the perfect selection on the first click. That’s because you’re making an intelligent guess about what Tolerance setting can pick up the pixels you want.
The Grow command compensates a little for the Magic Wand tool’s inaccuracy. For example, if you need to include more in your selection, you can increase the Tolerance setting and try again — hold down Shift and click the area you need to include. Or you can choose Select→Grow. The Grow command increases the size of the selection by including adjacent pixels that fall within the range of Tolerance.
The Similar command is like Grow, only the pixels don’t have to be adjacent to be selected. The command searches throughout the image and picks up pixels within the Tolerance range, wherever they may fall.
Both commands use the Tolerance value that’s displayed on the Options bar when you have the Magic Wand tool selected. Adjust the Tolerance setting to include more or fewer colors by increasing or decreasing the setting, respectively.
The Refine Edge command also helps to fine tune your selection.