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
(gp:read-external-image
file
:transparent-color-index 42)
(setf
(gp:external-image-transparent-color-index
external-image ) 42)
You can use an image tool such as 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.
CAPI User Guide (Unix version) - 30 Aug 2011