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

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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

(gp:read-external-image file :transparent-color-index 42)

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.


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

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