Levels can be used to make an image look lighter, darker, or more detailed. They can also be used to adjust color. A composite channel's brightness and tonal range can be adjusted to affect lightness and the appearance of detail, and an image's individual color channels can be adjusted to create a color shift in the image. This is one way an undesirable color cast may be removed.
Access the Levels dialog box in either of the following ways:
Click the Create a New Fill or Adjustment Layer button at the bottom of the Layers palette and choose Levels.
The Levels dialog box, shown in Figure 9.5, displays a histogram with values measured from 0 (black) to 255 (white) and a starting gamma (midtone) value of 1.00.
Numeric Input Levels are below the sliders, and numeric Output Levels are shown at the bottom of the dialog box. The Channel menu, which shows the composite RGB color channel, can be changed to cause a Levels adjustment to target individual color channels, such as Red, Green, or Blue. The Channel menu options will vary according to the color mode of the image.
Make Levels adjustments to an image by:
Dragging any of the sliders
Entering numeric input and output (before and after) values
Clicking in ...