History
Y'UV was invented when engineers wanted color television in a black-and-white infrastructure. They needed a signal transmission method that was compatible with black-and-white (B&W) TV while being able to add color. The luma component already existed as the black and white signal; they added the UV signal to this as a solution.
The UV representation of chrominance was chosen over straight R and B signals because U and V are color difference signals. This meant that in a black and white scene the U and V signals would be zero and only the Y' signal would need to be transmitted. If R and B were to have been used, these would have non-zero values even in a B&W scene, requiring all three data-carrying signals. This was important in the early days of color television, because holding the U and V signals to zero while connecting the black and white signal to Y' allowed color TV sets to display B&W TV without the additional expense and complexity of special B&W circuitry. In addition, black and white receivers could take the Y' signal and ignore the color signals, making Y'UV backward-compatible with all existing black-and-white equipment, input and output. It was necessary to assign a narrower bandwidth to the chrominance channel because there was no additional bandwidth available. If some of the luminance information arrived via the chrominance channel (as it would have if RB signals were used instead of differential UV signals), B&W resolution would have been compromised.
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