Using Adjustment Layers

When processing images, adjustments to properties such as color balance, levels, contrast, etc. can be make directly to the image. However, I prefer to make these changes using Adjustment Layers, because if I decide to edit the photo later, I can more easily see what changes I have made, and I can undo or edit them with no loss of data.

To show what I mean about loss of data, I'll use an extreme example of applying adjustments directly to an image:

Original Original Image
Very low contrast After Lowering Contrast

Now, you'd never lower the contrast this far, but as I said, this is an extreme example.
After trying to restore contrast After "Restoring" Contrast

Here's the result when we try to restore the contrast. You can see that a lot of the original data has been lost. The loss is most visible in the sky and the reflections.

With Adjustment Layers, however, all the original information is retained, so you can make any changes you want later, by just opening the adjustment layer and changing the settings. You can even delete an adjustment layer and start over.

Creating an Adjustment Layer

Creating an adjustment layer To create an adjustment layer, you can either use the Layer menu, or click this icon in the Layers window. Then just choose the type of adjustment you want to make, and make the changes.
Adjustment layer After you've created an adjustment layer, your Layers window will look something like this. In this case, the adjustment layer I created was for Selective Color. If you want to change the settings later, just double-click on the layer thumbnail (where the red arrow is pointing). You can then see the settings and edit them.

Notice that the Adjustment Layer has a mask (the rectangle to the right of the layer thumbnail) associated with it. If you want the adjustments to apply only to certain portions of the photo, you can control that by "painting" or "erasing" portions of the mask.

After you've made all your adjustments except for sharpening, save a copy of the file as a Photoshop PSD file. If you discover later that you don't like the results of your adjustments, you can easily change them without completely reprocessing the photo.

The downside? Adjustment Layers do make for larger files.