GB1519151A - Systems for processing a colour composite signal - Google Patents

Abstract

1519151 Television AMPEX CORP 19 June 1975 [28 June 1974 (2)] 26139/75 Heading H4F To eliminate timing errors from colour television signals of the NTSC type played back from a magnetic tape a luminance-coherent subcarrier reference signal is generated from the separated sync component and used to correct phase errors in the separated chrominance component or encode the separated colour components after they have been phase corrected in response to a subcarrier reference signal generated from bursts separated from the chrominance component. These methods of timing error correction ensure coherency of the signals horizontal sync and colour burst components (i.e. coherency of the luminance and chrominance components) and thus enable conventional line-to-line time base correction using a plurality of delay lines to be effected upon the resulting output signal. In Fig. 1 the composite colour television signal from a magnetic tape is separated into its luminance component (2À7 MHz high pass filter 9) and its chrominance component (767 KHz band pass filter 14-the chrominance component having been frequency-transposed before recording). The chrominance component is frequency-converted by balanced modulator 15 to its nominal frequency at 3À58 MHz in response to a 4À347 MHz input from balanced modulator 23 which receives the 767 KHz output of VCO 22 and 3À58 MHz output of subcarrier generator 10 (Fig. 2 not shown) controlled by the horizontal sync pulses separated 31 from the luminance component. VCO 22 is controlled by the output of phase detector 21 which receives the output of subcarrier generator 10 and the bursts separated 20 from the corrected chrominance component. Modulator 23 may be omitted if oscillator 22 has a nominal frequency of 4À347 MHz. The prior art system using a stable crystal reference oscillator 26 of 3À58 MHz may be modified to include the coherent subcarrier generator 10 by including switch 18. Two further embodiments are described with reference to Figs. 3 and 4 (not shown). In a fourth embodiment Fig. 5 band pass filter 83 of 3À58 MHz separates the chrominance component from the luminance component. This chrominance component is decoded into I and Q signals in response to a VCO 88 controlled by a phase detector 87 in response to the separated bursts 85, to thereby eliminate phase errors. These I and Q signals are then encoded 89 onto a sync coherent subcarrier from generator 10 in response to line sync pulses separated from the luminance component.