Adjustment layers are simply layers without any image pixels. These special layers can store the directions for color or tone adjustments or can store a layer mask. The layer mask can be clear, which causes all of the adjustment layer’s changes to be applied to the image pixels of the layer directly beneath it. Or, your adjustment layer can have grayscale info that keeps the adjustment layer’s changes restricted to only the areas you choose. You can also make your adjustment layers part of a group, thus making the adjustments effective only on the layers in the group.
Making an adjustment layer is easy. In Photoshop CS2, you just click on the adjustment layer icon at the bottom of your layers palette. (The icon looks like a circle, divvied down the middle, half colored black, the other half white.) A menu will pop up, giving you all of the adjustment layer options. You just choose one and a new adjustment layer is made, directly above the active layer. Depending on the option you choose, a window will pop up on your screen giving you the different options related to each adjustment layer type. Below are the different types of adjustment layers that you can choose.
Solid Color: This one is pretty simple. It just creates a layer that is filled with a solid color. A window pops up so you can choose which color you want the layer to be filled with.
Gradient: This creates a layer that is filled with the gradient that you choose with the gradient fill options that pop up when the adjustment layer is made.
Pattern: This creates a layer that is filled with a pattern that you choose with the pattern fill options that pop up when the adjustment layer is made.
Levels: This creates an adjustment layer that allows you to change the white and black points and output levels to adjust the tonal range and color balance in your images.
Curves: This creates an adjustment layer that let’s you change the color balance and lighten or darken your image.
Color Balance: This layer allows you to adjust the tone and color of your shadows, midtones or highlights. You can use this adjustment layer for color general color correction or to create special effects in your images.
Brightness/Contrast: This creates an adjustment layer allowing you to change the brightness or contrast of your images.
Hue/Saturation: This adjustment layer allows you to change the hue, saturation and lightness of your images. The adjustments can be made on all of the colors or on each color channel individually. You can check the colorize option to color your photo with the hue of your choice, making it easy to change a color photo to a sepia effect or any other color you choose.
Selective color: This adjustment layer allows you the option to adjust the color levels in each individual channel. You could use this option for detailed color correction or if you just want to change the color of something in your image.
Channel Mixer: This creates an adjustment layer that allows for numerous color adjustments and corrections. You can create a radical change to your colors, add sepia tones, make your image pastel or use it to get a good grayscale image from a color photo. There are many options that you can experiment with in the channel mixer to get just the effect you want.
Gradient Map: This adjustment layer maps the grayscale range of an image to the colors of a specified gradient fill. In a two-color gradient fill shadows are changed to one of the endpoint colors of the gradient fill, highlights are changed to the other endpoint color, and midtones are changed to the gradations in between.
Photo Filter: This allows you to filter the colors of your image similar to putting a color filter on your camera when taking a photo. The photo filter options allow you to warm or cool your overall image, add a sepia tone or any other color tone that you choose.
Invert: This creates a layer that inverts the colors of your images. This would be useful in masking your image for sharpening or other adjustments. This is also just a cool effect.
Threshold: This adjustment layer allows you to easily see the image’s highlight and shadow values. By moving the slider to the right or left you can determine the white and black points in your image.
Posterize: This creates an adjustment layer that allows you to choose the number of tonal levels in your color or grayscale image. For example choosing three tonal levels would change your RGB image to nine colors, three in each color channel. This is useful for creating special effects in your images.
This is just a quick overview of adjustment layers and their options. You can use them experiment with your images to find many more ways to use the various options that Photoshop gives you in editing your photos. Consider adding a tan to your shade-loving hubby in your vacation photos, or changing the color of your dog. You could even use adjustment layers to emphasize the lights in your Christmas photos or to easily experiment with different tonal effects, like sepia or grayscale, without messing up your original.