getting started with photoshop - Using the Gradient Map command

Using the Gradient Map command 

The Gradient Map command maps the equivalent grayscale range of an image to the colors of a specified gradient fill. If you specify a two-color gradient fill, for example, shadows in the image map to one of the endpoint colors of the gradient fill, highlights map to the other endpoint color, and midtones map to the gradations in between.

To use the Gradient Map command:

1. Open the Gradient Map dialog box.

2. Specify the gradient fill you want to use:

• To choose from a list of gradient fills, click the triangle to the right of the gradient fill displayed in the Gradient Map dialog box. Click to select the desired gradient fill, and then click in a blank area of the dialog box to dismiss the list.
• To edit the gradient fill currently displayed in the Gradient Map dialog box, click the gradient fill. Then modify the existing gradient fill or create a new gradient fill.

By default, the shadows, midtones, and highlights of the image are mapped respectively to the starting (left) color, midpoint, and ending (right) color of the gradient fill.

3. Select either, none, or both of the Gradient Options:
• Dither adds random noise to smooth the appearance of the gradient fill and reduce banding effects.
• Reverse switches the direction of the gradient fill, reversing the gradient map.