12.8.2.1 Transparency

An External Image representing an image with a color map can specify a transparent color. When converted and drawn, this color is drawn using the background color of the port.

You can specify the transparent color by

or by

(setf 

 (gp:external-image-transparent-color-index external-image
) 

 42)

You can use an image tool such as the Gimp ( www.gimp.org ) to figure out the transparent color index.

Note: transparent-color-index works only for images with a color map - those with 256 colors or less.