| 摘要 |
In certain video scrambling systems, composite video is imperfectly separate d into luminance and chrominance and scrambled in such a way that an unstable residual chroma color subcarrier remains in the luminance channel. When this unstable residual subcarrier subsequently is summed with stabilized chroma, the resultant composite color signal has small but visible amounts of color subcarrier instability that causes a noisy color signal when descrambled or when displayed on a television display device. A coring circuit is disclosed which provides means for substantially removing the unstable residual chroma subcarrier from the luminance channel, thereby substantially reducing color subcarrier instabilities. An improved coring technique also is disclosed usi ng adaptive chroma coring, which is achieved by adjusting the amount of coring applied in accordance with the amplitude of the chrominance signal. Thus, if the program video input has high levels of color saturation, the chroma cori ng is electronically turned up. Conversely, if the input video program is essentially in black and white (no color content), then the coring circuit essentially is electronically turned off. The coring techniques also are applicable to enhance the luminance-chrominance separation of video comb filters frequentlyused in video circuits such as, for example, television sets and video recorders.
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