The television signal wave form is actually a composite made up of three individual signals, as is shown in the figure. The first is a continuous sequence of electrical values corresponding to the brightnesses along each line. This signal contains what is known as the luminance information. The luminance signal is interspersed with blanking pulses, which correspond to the times during which the scanning spot is inactivated and retraced from the end of one line to the beginning of the next, as described above. Superimposed on the blanking pulses are additional short pulses corresponding to the synchronization signals (also described above), whose purpose is to cause the scanning spots at the transmitter and receiver to retrace to the next line at precisely the same instant. These three individual signals—luminance, blanking, and synchronization—are added together to produce the composite video signal.
