Composite and Components Video

--------------------------------------------------------------------------------

Composite and Components Video


The common television receiver found in many homes receives from the transmitter a composite signal, where the luminance and chrominance components [Salomon 99] are multiplexed. This type of signal was designed in the early 1950s, when color was added to television transmissions. The basic black-and-white signal becomes the luminance (Y ) component, and two chrominance components C1 and C2 are added. Those can be U and V , Cb and Cr, I and Q, or any other chrominance components. Figure 6.5a shows the main components of a transmitter and a receiver using a composite signal. The main point is that only one signal is needed. If the signal is sent on the air, only one frequency is needed. If it is sent on a cable, only one cable is used.

Composite video is cheap but has problems such as cross-luminance and crosschrominance artifacts in the displayed image. High-quality video systems normally use component video, where three cables or three frequencies carry the individual color components (Figure 6.5b). A common component video standard is the ITU-R recommendation 601, which uses the YCbCr color space (page 626). In this standard, the luminance Y has values in the range [16, 235], whereas each of the two chrominance components has values in the range [16, 240] centered at 128, which indicates zero chrominance.