Color television chroma keying signal generator
First Claim
1. A colour television chroma keying signal generator comprising a matrix circuit means for supplying to an output a colour signal combination of colour signals supplied to inputs thereof, two signal combination and multiplication circuits coupled to the matrix circuit output, each having an adjustable multiplication factor and output means for providing colour difference signals, a signal adder circuit means coupled to said output means for forming a composite colour difference signal, and a chromaticity signal operated threshold circuit means coupled to the adder circuit for supplying a chroma keying signal to an output of the generator.
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Abstract
A chroma keying signal generator which does not operate in the usual manner with luminance dependent color difference signals (R-Y) and (B-Y) but with luminance independent chromaticity signals (R-Y)/Y and (B-Y)/Y. On the one hand a signal division may follow in the generator for deriving the chromaticity signals and on the other hand a threshold circuit may be used having a threshold voltage which varies with the luminance. Owing to the fact that generating the signal is independent of the luminance an intense, uniform background illumination without shadows thereon is no longer required.
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Citations
6 Claims
- 1. A colour television chroma keying signal generator comprising a matrix circuit means for supplying to an output a colour signal combination of colour signals supplied to inputs thereof, two signal combination and multiplication circuits coupled to the matrix circuit output, each having an adjustable multiplication factor and output means for providing colour difference signals, a signal adder circuit means coupled to said output means for forming a composite colour difference signal, and a chromaticity signal operated threshold circuit means coupled to the adder circuit for supplying a chroma keying signal to an output of the generator.
Specification