One of the many things that makes Photoshop so powerful is its ability to facilitate nondestructive image editing. Traditionally, anytime a pixel is altered—even if it’s just an adjustment to its luminance or color—image data has been modified in a way that can’t be undone. Additional edits degrade data even more, and soon enough, the subtle detail, particularly in highlights and shadows, is lost.
By comparison, nondestructive editing doesn’t alter a file’s original image-forming data. The pixels that make up an image are untouched, and every edit is made virtually. This provides for powerful processing that doesn’t degrade image quality, as well as the unlimited capacity to refine and undo every edit down the line. (This is the idea behind the adjustments in photo-editing tools like Lightroom and Apple’s former Aperture, as well.)
Photoshop’s most powerful nondestructive editing tool may be the Adjustment Layer. These specialized layers can alter color, contrast, brightness—practically any adjustment to a pixel you can imagine—without changing the original image’s data.
Adjustment layers include these specific controls: Brightness/Contrast, Levels, Curves, Exposure, Vibrance, Hue/Saturation, Color Balance, Black & White, Photo Filter, Channel Mixer, Color Lookup, Invert, Posterize, Threshold, Selective Color and Gradient Map. If you’re familiar with any of these adjustments as found in the Image menu, you’re familiar with how they will work as adjustment layers, too.
To create an adjustment layer, you can use the Adjustment Layers palette for one-click access to the specific adjustment you’d like, or if you don’t have the Adjustment Layers palette open on your screen, you can click the black/white circle icon at the bottom of the Layers palette to open a drop-down menu listing all of the available adjustment layers. Choose your preferred option, name the layer, if you care to, and click OK.
By default, adjustment layers apply to all of the layers below them. This is helpful because it can speed the editing workflow on a multilayered image. If you want to isolate an adjustment layer strictly to the layer immediately below, there’s a method for that, too.
Say, for instance, you have a subject isolated on its own layer and the background on another layer. Simply click the “down arrow” icon at the bottom of the Adjustment Layers palette and the adjustment will be clipped to the layer immediately below, and it won’t have any impact on any of the other layers.
To apply an adjustment layer to multiple layers, but not all layers, create a Group (Command+G or use the Create a New Group icon at the bottom of the Layers palette) and then clip the adjustment layer to only that group using the same “down arrow” icon.
Another advantage provided by adjustment layers is that the individual adjustments can be selectively applied with layer masks. By default, when an adjustment layer is created, it’s accompanied by an empty layer mask. Painting on the mask refines the area where the layer’s adjustment will be applied—whether that’s the whole layer, none of the layer or any of the pixels in between.
One particular way I like to use adjustment layers is to fade them from one side of the scene to the other or from the bottom to the top. This can be very helpful for, say, evening out background illumination or darkening the bottom half of the frame to draw the eye to the center of attention more directly with a Levels or Curves adjustment layer. Either way, I make this edit by using a gradient fill on the layer mask.
Click on the Gradient tool (hidden beneath the fill Paint Bucket tool on the Tool palette) and click on the adjustment layer’s layer mask icon in the Layers palette to activate the mask. This will default the foreground and background colors to black and white—which, when applied to the layer mask, will read as opacity or transparency. You then can click and drag the Gradient tool from top to bottom or side to side to establish a gradient from clear to opaque and apply the adjustment layer selectively to one portion of the scene. The longer the click-and-drag of the Gradient tool, the softer and smoother the transition from opaque to transparent. The shorter that click-and-drag, the harder and faster that transition.
Adjustment layers can be modified, like any other layer, by adjusting the opacity and blending mode to alter the impact. They also can be copied from one image and applied to another and another, making quick changes to a group of images quick and painless.
Some of my personal favorite uses for adjustment layers include the following:
• The Photo Filter, set to Warming Filter 85 and an opacity of anywhere between 5% and 25%, is a great way to add a touch of warmth to a portrait—something that’s often quite useful.
• Levels and Curves are a wonderful way to make adjustments to contrast and brightness, as well as to isolate tonal values in shadows, midtones and highlights.
• The Black & White adjustment layer is the way to convert a color image to black-and-white. After clicking on the Black & White icon, use the color sliders to adjust the brightness and influence of each color in the black and white mix. Or, you can use the drop-down menu for a variety of preselected black and white mixes. If one recipe works better on one part of the frame and another mix works better on a different area, a layer mask followed by a second adjustment layer with a different black and white mix is the perfect way to get super-customized monochrome conversions.
• The Color Lookup adjustment layer got its start in the video world, but these filters work great for making special effects in still photographs, too. Technically speaking, color lookup tables map colors and tonal values to a new space, creating sometimes subtle effects and other times wild and wacky ones.
• For selectively altering a specific color in an image—the red of a lipstick, for instance, or the green leaves in a landscape—the Hue/Saturation adjustment layer is my first stop. I first select the color I’d like to modify using the drop-down menu in the adjustment layer’s pop-up palette, and then I adjust it brighter or darker, more saturated or less, to ge
t exactly the appearance I’m after. If the effect needs to be isolated, painting on the layer mask works perfectly. And, best of all, it easily can be modified later, as needed.
William Sawalich is a commercial photographer, an educator and a contributing editor for Digital Photo, Digital Photo Pro and Outdoor Photographer magazines. Since 1998, he has written hundreds of equipment reviews, how-to articles and profiles of world-class photographers. See more of his work on his website at sawalich.com.