Mapping colors to transparency
You can add transparency to an optimized image by mapping existing colors to transparency.
To map colors to transparency:
- Select one or more colors in the optimized image or color table. (See Selecting colors.)
- Do one of the following:
- Click the Map Transparency button
in the Color Table palette. - Choose Map Selected Colors to Transparent from the Color Table palette menu.
The transparency grid 
appears in half of each mapped color. The small square at the lower right of the color swatch indicates that the color is locked.
To revert transparency to its original colors:
- Select the colors you want to revert and click the Map Transparency button or choose Unmap Selected Colors from Transparent from the Color Table palette menu.
- To revert all transparency-mapped colors, choose Unmap All Transparent Colors.
Do one of the following: