| 摘要 |
A chroma-key circuit is described for use in alternately selecting one of two TV camera outputs to provide a composite picture, wherein the selection is controlled by detecting changes between a background color and an object color sensed by one of the two cameras. Keying is accomplished digitally by comparing the phase of the chrominance signal from the one camera with the phase of a reference signal, and by switching the circuitry to transmit the signal from the one camera only when the chrominance and reference signals are out of synchronization.
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