Limitations of Adjustment Layers

There is one limitation of Adjustment Layers that prevent certain adjustments from being available as an Adjustment Layer. An Adjustment Layer must be able to be fed a single pixel and figure out how it should be modified without having to rely on the information contained in the surrounding image. The Match Color, Replace Color, Shadow/Highlight, Exposure, and Equalize adjustments must be able to compare the area being adjusted to the surrounding image (or a second image) to determine how to adjust the image, which prevents them from being used as Adjustment Layers.

There are five other adjustments that are not found in the Adjustment Layers pop-up menu at the bottom of the Layers palette: Auto Levels, Auto Contrast, Auto Color, Desaturate, and Variables. These are really shortcuts for using adjustments in certain ways. You can use the following equivalents to get the same functionality in an Adjustment Layer:

• Auto Levels is the same as clicking on the Options button in the Levels or Curves dialog box and choosing the Enhance Per Channel Contrast, while leaving the other settings at their defaults.

• Auto Contrast is the same as clicking on the Options button in the Levels or Curves dialog box and choosing the Enhance Monochromatic Contrast, while leaving the other settings at their defaults.

• Auto Color is the same as clicking on the Options button in the Levels or Curves dialog box and choosing the Find Dark & Light Colors, while leaving the other settings at their defaults.

• Desaturate is the same as moving the Saturation slider in the Hue/Saturation dialog box to -100.

• Variations is a visual interface for a combination of the Saturation slider in Hue/Saturation, the Brightness slider in Brightness/Contrast and the choices available in the Color Balance dialog box.