GB1142944A - Line sequential color television systems - Google Patents

Abstract

1,142,944. Colour television. GENERAL CORP. 22 Feb., 1966 [27 Feb., 1965], No. 7632/66. Heading H4F. In a three-colour line-sequential colour system using odd line interlaced scanning (i.e. two fields per frame) and a number of lines per frame which is not an integral multiple of three (625 in the system disclosed) the colour sequence is not continuous but is controlled as shown in Fig. 5, so that the sequence is interrupted and restarted with a predetermined colour (i.e. red) at the second line of the first field of each frame and with the same colour at the first line of each second field. By this means the crawling colour pattern which occurs with a continuous sequence is eliminated. The control of the sequence is effected as illustrated in Fig. 19 by separating the odd and even field synchronizing signals, delaying the odd signals for the duration of one line and then recombining the signals to form a composite signal train which controls both the start of the colour sequence and the production of a colour synchronizing " burst " for insertion in the back porch interval preceding each red line. The invention is described as applied to a system, Fig. 14 (not shown), in which received N.T.S.C. signals are converted to linesequential signals, which are recorded magnetically and subsequently reproduced by a line-sequential receiver using a post-deflection, beam-switching, cathode-ray tube. The conversion of the N.T.S.C. signal is effected by demodulating the chrominance subcarrier component with a reference oscillation which is modulated so as to change phase in line sequence to the three angles which are necessary to obtain the colour difference signals R-Y, G-Y and B-Y. These signals are then combined with the luminance signal to form a normal line-sequential signal. The phase modulation of the reference oscillation is produced by a three-step wave which is generated under the control of the received horizontal synchronizing pulses and started in correct phase in each field by the odd and even field synchronizing signals in the manner described above with reference to Fig. 19. The synchronizing " bursts " which are added to the signal before each red line have a frequency (e.g. 2 Mc/s.) within the recording capability of a magnetic recorder. Suitable arrangements for separating the odd and even field synchronizing signals are described with reference to Figs. 8-12 (not shown). In the line-sequential colour receiver for use with the system the colour switching grids of the cathode-ray tube are controlled by a three-step wave, similar to that shown in Fig. 19, which is derived under the control of horizontal synchronizing pulses and established in the correct phase by the synchronizing " bursts ". In arrangements in which the number of scanning lines leaves two after division by three the odd field synchronizing signal may be advanced in time by one line period or the even field signal may be delayed by one line period.