The initials RGB stand for the three primary colors used for television screen presentations: red, green and blue. Both analog and digital signals carry this information, but analog has been in use longer. Home entertainment system users, marketers and manufacturers use the term RGB loosely to describe various types of formats, connections and cables.
An analog signal produces a waveform that varies in level from zero to a positive value, back down to zero and crossing it to a negative value and then returning to zero. The number of times it does this in a second measures its frequency, expressed in hertz or Hz. Analog RGB signals carry video information for the three primary video colors on separate signals, one for each color. Formats that use analog waveforms for RGB signals in home entertainment systems include component video and video graphics array.
Because component video identifies its three cable connections with the colors red, green and blue, many users mistakenly call the format analog RGB. Manufacturers color code RCA plugs and jacks green for the Y signal, which carries synchronization information along with the green signal. They color code plugs and jacks for the Cr or Pr signal red because they carry the red signal, and the Cb or Pb blue for the blue signal. The format is also called YCrCb or YPrPb, depending on the country in which it is used.
Because video graphics array also sends three discrete video color signals, users again mistakenly call it analog RGB. However instead of traveling on three single cables, VGA travels on a single cable with 15-pin connectors, but does not include the synchronization on the green signal. It sends separate horizontal and vertical sync signals on additional wires in the cable. A VGA cable also carries control signals from the monitor back to the signal source for various information and controls. Because of the five separate signals, sometimes users call it RGBHV.
Professional Analog RGB
In professional settings, analog RGB video signals travel in similar formats, but with BNC twist-on connectors on the individual cables. Professional RGB, much like composite video, carries the sync signal with the green, but the formats are not compatible. RGBS takes the sync off the green and puts it on a fourth cable. RGBHV uses five cables to separate horizontal and vertical synchronization signals, but provides no signal path from the monitor back to the source. RGBHV is only compatible with VGA in cases where the return path is not needed.