nondestructive

It's difficult (verging on impossible) to exaggerate the importance of color adjustments in Photoshop. In the 19+ years I've been using the program, I don't think I've come across a single image that I haven't adjusted to some degree or other. And while there's no single best command for adjusting colors (Feature #28: Hue/Saturation for one image, Feature #24: Curves for another), there is a best method: adjustment layers.

An adjustment layer is an independent layer of color adjustment that you can edit any time you like. Plus it affects all layers below it, consumes very little space in memory, and affords you the opportunity to make selective edits. In other words, it's small and nondestructive. (Compare this to Feature #18: Smart Objects, which is huge and nondestructive.) The modest adjustment layer is also relatively easy to use--by Photoshop standards, anyway. Read more » 

Do me a brief favor and ignore this feature's name. Smart objects aren't all that smart. And they aren't objects. In other words, smart objects aren't "smart objects."

What "smart objects" are is envelopes. The kind that hold things. And keep them safe. Place an image or vector file into one of these envelopes, and nothing you do can cause that file harm. Which means you can apply nondestructive transformations, nondestructive filters, nondestructive everything. The world is your pixel-based oyster. Read more »