Dynamic hue control networks

Abstract

Poor transmission characteristics generally produce hue errors at low luminance levels. This comes about because of differential gain and phase effects in the transmission path between the modulator of the transmitter and the demodulator of the receiver. The hue control may be set such that high luminance flesh colors will be acceptably correct, but the dark areas often are incorrect with objectionable green tinges being present, especially in close-ups of dark skin, hair and shadow areas. This problem is overcome by automatically increasing the demodulation angle at low luminance levels. A signal that varies in accordance with the luminance level automatically adjusts a phase shift network to effect a phase shift of the chrominance signal relative to the reference signal or vice versa prior to these signals being applied to the chroma demodulators.