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Introduction to composite NTSC and PAL
In component video, the three colour components are kept separate. Video can use R’G’B’ components directly, but three signals are expensive to record, process, or transmit. Luma (Y’) and colour difference components based upon B’-Y’ and R’-Y’ can be used to enable subsampling: Luma is maintained at full data rate, and the two colour difference components are subsampled. Even after chroma subsampling, video has a fairly high information rate (data rate, or “bandwidth”). To further reduce the information rate, the composite NTSC and PAL colour coding schemes use quadrature modulation to combine the two colour difference components into a single modulated chroma signal, then use frequency interleaving
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