In the RGB color model, all three channels contribute to the perception of brightness.
In the early 1950s, this was a problem when developing a three-channel color television
system that would be compatible with existing black-and-white televisions. The
solution was to encode a single channel that represented luminance—light intensity as
perceived by humans—which existing black-and-white televisions could decode. Color
televisions would receive the same luminance channel and two additional color
channels that could be decoded back into RGB color for display.