In addition to the scanning and channels of black-and-white TV distinguished by Latin letters, different color TV formats are formed according to different coding and decoding methods of tricolor signals at the transmitter and receiver. Broadcast color TV system requires compatibility with black-and-white TV, that is, black-and-white TV can receive color TV broadcasts, and color TV can also receive black-and-white TV broadcasts, but all they receive are black-and-white images and accompanying sounds. Therefore, according to the principle of mixing a certain proportion of light energy of three primary colors into various color lights including white light, in order to be compatible with and compress the transmission band, color TV sets generally combine three primary color signals of red (R), green (G) and blue (B) into a brightness signal (Y) and two color difference signals of blue and red (B-Y, R-Y), where the brightness signal can be.
Therefore, compatible color TV not only transmits the same brightness signal and sound signal as black-and-white TV, but also transmits the same color signal of video frequency band. The chroma signal is formed by modulating the color subcarriers at the high frequency end of the video band with two color difference signals. In order to prevent the modulation overload of the color difference signal, the blue and red difference signals (B-Y) and (R-Y) are compressed, and the compressed blue and red difference signals are represented by U and V. ..