| 摘要 |
1503896 Chrome keying signal generator PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 17 Aug 1976 [20 Aug 1975] 34210/76 Heading H4F Colour television chroma keying signal generator comprises a matrix circuit M producing luminance signal Y from the foreground camera outputs R, G and B; combination and multiplication circuits 6 and 8 supplied with adjustable voltageαand producing outputs (R-Y)sinαand (B-Y)cosαwhich are added 10, black level clamped 14 and compared 17 with the black level clamped 15 luminance signal Y multiplied 12 by adjustable voltage input c. The output of comparator 17 is logic 1 (i.e. a chroma keying signal CK is produced) when Thus the chroma keying signal is derived from chromaticity signals (R - Y)/Y and (B - Y)/Y i.e. it is independent of brightness variations. Since at low levels of brightness (low Y) noise could cause a chroma keying signal to be generated by comparator 17, a second comparator 18 is provided which receives and a minimum threshold voltage d. The outputs of comparators 17 and 18 are fed to an AND gate 20 so that a chroma keying signal CK is produced when Instead of using Y any other colour signal combination may be used. Two such arrangements may be used in parallel with different adjustable anglesαand #. |
