RGBI to multilevel grey scale encoder

[nikoniko]

Greyscale composite derived from RGBI. I haven't studied it closely, but it sounded like rather than determining deriving luminance from the color and intensity, the 4 bits of RGBI are used as a binary index to a 16 level greyscale. If so, programs would need to be specifically written to account for that scheme if one applied this design. 16 levels *would* be nice, but perhaps not worth the trouble.

http://www.google.com/patents?id=BIgsAAAAEBAJ&dq=4739312

RGBI to multilevel grey scale encoder

United States Patent    4,739,312
Oudshoorn ,   et al.    April 19, 1988

Abstract

An encoder (500) encodes a TTL type of R,G,B,I video drive signal into a common multilevel grey scale digitally encoded composite video signal which is transmitted over a single coaxial cable (302). The incoming R,G,B,I bits, such as provided from a color computer (304, 306, 308, 310), are buffered and translated (50a, 50b) from TTL to ECL and fed to a common video digital-to-analog converter (100) along with translated composite sync information (312, 314, 10, 324). A white reference level signal is dynamically derived from the translated sync information (200, 202) and provided to the full height input of the video D/A converter (324, 100) which converts the translated R,G,B,I input into a 16 level multibit grey scale code in a linear function from full intensity white to black, with a seventeenth level being provided in the digitally encoded composite video signal to represent sync information.