| 摘要 |
To provide an improved non-additive mixer, a first mixer mixes first and second video signals according to a mixer control signal derived in a new way. The first and second video signals are applied, respectively, to first and second chrominance (blocking) filters. The resulting first and second luminance signals are applied, respectively, to first and second summing circuits, where offsets may be applied to either or both of them. The difference is then taken between the first offset luminance signal and the second offset luminance signal to produce a difference luminance signal. The difference luminance signal is then multiplied by a gain control signal to produce the mixer control signal. The mixer control signal can also be used to control a second mixer, thereby providing a channel for keying information that is non-additively mixed according to the luminance content of the video signal that the key information is associated with.
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