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Color Television

Monochrome television involves a single signal: brightness, or luma, usually given the symbol Y. (Although more properly it’s Y’, a gamma-corrected value.) Color TV requires three times the information: red, green, and blue (RGB). Unfortunately, color TV was supposed to be broadcast using the same spectrum as monochrome, using the same bandwidth, so having three times the information was a bit of a problem.

Engineers at RCA developed a truly brilliant solution. They realized that the frequency spectrum of a television signal had gaps in it largely unoccupied by picture content. They encoded color information in a sine-wave called a subcarrier and added it to the existing luma signal; the subcarrier’s frequency fit within one of the empty gaps in monochrome’s spectrum, so the luma information was largely unaffected by the new chroma information, and vice versa. The resulting signal remained compatible with existing monochrome receivers and fit in the same broadcast channels: they had managed to squeeze the quart of color information into the pint pot of existing monochrome broadcasting.


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