Using the Gradient Map Adjustment
The Gradient Map adjustment replaces the tonal values of the image with the colors supplied by a gradient. It's a great tool for generating special color effects. In addition, the Gradient Map adjusts the active image's colors to the colors of the selected gradient; taking the shadows of the image and mapping them to one endpoint of the gradient, and the highlights to the other point.

Use the Gradient Map Adjustment
Open an image.
Click the Image menu, point to Adjustments , and then click Gradient Map .
Click the Gradient Used For Grayscale Mapping list arrow to adjust the gradient.
Select or clear the Dither or Reverse check boxes for the Gradient Options.
Select the Preview check box to view changes to the active image.
Click OK .
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