Abstract: A detection system for automatically detecting a first light transmissive substance in a second and different light transmissive substance. An optical system is arranged for alternately producing light beam flashes of light having a first wavelength and light having a second wavelength to the input of an opto-electric detector. A volume containing the first and the second substance can be selectively positioned at the output side of said optical means in front of the opto-electric detector. The opto-electric detector delivers its electrical signals corresponding to the light beam flashes received thereby, to a electrical detecting arrangement. The electrical detecting arrangement comprises first means for producing a first voltage proportional to the ratio between light transmitted through the volume under inspection at the first wavelength and light transmitted through the volume under inspection at the second wavelength, and second means for producing a second voltage indicative of a threshold level.

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.