To Specify a Transparent Color From the Color Table

1. On the ribbon, click Raster Tools tab Edit panel Process Image drop-down menu Palette Manager.

   The Palette Manager dialog box is displayed.

2. Select a color from the color table or use the Select Color button to pick a color directly from the image. For more information, see Selecting a Color Directly from the Image.
3. Click the Background Transparent button, or right-click and select Set Background Transparency on the shortcut menu.
4. To turn on background transparency in the image, select the Background Transparency check box and click Apply.
5. Click OK to close the Palette Manager dialog box.
   Note: If the Background Transparency check box is cleared, the background transparency will not appear.