GB1342913A - Colour signal decoding - Google Patents

Abstract

1342913 Colour television MOTOROLA Inc 19 April 1971 [5 Feb 1970] 20923/71 Heading H4F A photographic film, magnetic tape or embossed strip has luminance and chrominance information on adjacent frames, the chrominance information being recorded in the form of (for films) alternate opaque and transparent stripes, the width of the transparent stripes representing colour saturation, every second transparent stripe representing R-Y colour information, the intervening stripes representing B-Y colour information. The film 10 is scanned by a flying spot scanner 30 and the output chrominance signal 65 is passed to a clamp circuit 66 which clamps one set of peaks of signal 65 to provide signal 67 which is passed to a differential amplifier 75 and an envelope detector 70, half the output from which is also fed to amplifier 75. The resulting output is clipped and passed to a differentiator 80, the output from which controls a multivibrator 90 and phase splitter 92, to control gates 82, 84 to pass red and blue colour difference signals respectively, which are then integrated in circuits 102, 104. To achieve synchronization at the start of each line, trigger 124 is set by a horizontal retrace pulse 120 to interrupt the operation of multivibrator 90. The trigger 124 is reset and multivibrator 90 started by the next pulse from amplifier 75, which is one of a number of pulses recorded at the start of each line in phase with the red colour difference signals. Shading of the output luminance signal is compensated for by taking the output of envelope detector 70 and feeding it to scanner 30 to control the brightness of the raster, or to a shading circuit 114 which shades the chrominance signals the same as the corresponding luminance signal. In an alternative embodiment (Fig. 4, not shown) the negative output pulses of the differentiator 80 are passed by the gates 82, 84 instead of the chrominance signal, the gating signals 94, 96 from phase splitter 92 being integrated, and gated to the output of the apparatus when a pulse is received from gate 82 or 84, the amplitude of this integrated signal being a measure of the width of the associated stripe. In this case trigger 124 is reset by an oscillating signal built up in a resonant circuit by the recorded synchronizing pulses.