Most Adobe Photoshop users know you can use selection to confine your painting, filters, and editing to a specific area of an image. However, you may not know you can use the Preserve Transparency option on the Layers palette to accomplish the same goal.

For example, to modify an object (add special effects, apply color, or manipulate tonal levels) without affecting the areas of the layer in the transparent area outside an object, first choose Window, Show Layers to display the Layers palette. Then, activate the target layer and select the Preserve Transparency check box. Now you can paint or apply any modification to the layer without affecting the transparent area outside the existing object.