A video mixing apparatus carries out a chromakey process producing less degradation
of picture quality by generating a key signal which separates a foreground object
component from a screen component by using luminance information. In a three-dimensional
color space, a smaller oval body surrounding a region where the foreground object
is distributed and a larger oval body surrounding the smaller one are set. These
two oval bodies and a distribution of a source video signal determine a key signal
distribution. Key signal K=0 (zero) when the source video signal is inside the
smaller oval body, and K=1 (one) when the signal is outside the larger oval body.
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