LispWorks CAPI User Guide > 12 Graphics Ports > 12.8 Working with images > 12.8.2 External images

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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)

or by

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

You can use an image tool such as the Gimp ( ) 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.

LispWorks CAPI User Guide (Windows version) - 22 Dec 2009