Method and apparatus for overlaying digitally generated graphics over an analog video signal

摘要

A system for overlaying digital character signals on an analog video source signal including a predetermined color subcarrier includes a digital character generating device, a digital video encoder, and a switching device. The digital character generating device detects horizontal and vertical timing of pixel information in the analog video source signal, and generates digital character signals that are to be overlaid in predetermined pixels of the analog video source signal. The digital video encoder is responsive to the color subcarrier signal for generating a separate color subcarrier which is locked to the predetermined color subcarrier of the analog video source signal. The digital video encoder also converts the digital character signals from the digital character generating device into an analog video output signal that includes the color subcarrier generated in the digital video encoder. The swithching device directs the analog video output signal from the digital video encoder or the analog video source signal to an output of the system during pixels times when a digital character is to be overlaid or not overlaid, respectively, on the analog video source signal.