GB1151726A - Improvements in or relating to colour television systems. - Google Patents

Abstract

1,151,726. Colour television. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. 31 May, 1966 [12 June, 1965], No. 24061/66. Heading H4F. The invention relates to a colour television system in which there are transmitted colour synchronizing "bursts" of colour carrier oscillation during the horizontal back porch intervals, the "bursts" including a component the phase of which is reversed in alternate lines. To prevent the "bursts" from interfering with vertical scan synchronization they are blanked for an interval including the vertical synchronizing signal and the immediately preceding and following equalizing pulses. Where scanning proceeds on the conventional interlaced basis with an odd number of lines forming a picture made up of two frames, there results an operation such that, in a sequence of four frames, the last "burst" before the blanked interval is of one phase in two of the frames and of the opposite phase in the other two frames. The first "burst" after the blanked interval exhibits a similar phase variation. The effect of the interruption of the "bursts" on the colour synchronization at a receiver is not by itself serious and results in only a small saturation error. The phase variation in the "bursts" however causes the error to vary and results in undesirable lowfrequency flicker (e.g. of 12À5 c/s.) in the first (the upper) part of the reproduced picture following the blanked interval. In accordance with the invention this defect is eliminated by causing the last "burst" before the blanked interval and/or the first "burst" after the interval to have the same phase in all frames. In one way of achieving this Fig. 1 and 3, the blanking signal is arranged to be advanced in time in the sequence of four frames by one half of a line duration for three successive frames and then to be retarded by one and a half lines for the fourth frame. The "burst" signals F both immediately preceding and following the blanked interval then have the same phase in all frames. In another way of carrying out the invention (not illustrated) the phase alternation of a few "bursts" before and/or after the blanked interval is terminated.