a) Defines the amount of incident light that passes through a surface. Both ambient and diffuse light falling on a transparent polygon are transmitted through the polygon, but highlights are not. In paint systems, a similar property called “opacity” determines how opaque the paint loaded on the artist’s brush really is. b) Full-color mode makes it possible for a polygon to be translucent by assigning a transparency between 0% and 100% (0 = opaque, 100 = fully transparent). To implement transparency, we assume that a semi-transparent polygon covers only a fraction of each pixel which it covers. The final pixel’s value is a blend of the background and the polygon. Again, color maps have too few colors to do this. c) A feature in Indeo Video interactive codec in which software emulates chroma keying, allowing foreground video objects to be composited dynamically over a different background, a bitmap or possibly even another video. See Chroma Key.