Apparatus for combining video signals from a video source, such as a video disc player, with computer-generated graphics/text output on a single display, for overlaying the two. The computer-generated video is provided in RGB format; the other video is converted to RGB format if not already in that form...http://www.google.com.au/patents/US4498098?utm_source=gb-gplus-sharePatent US4498098 - Apparatus for combining a video signal with graphics and text from a computer
