GB1533238A - Split-screen television apparatus - Google Patents

Abstract

1533238 Television POST OFFICE 23 Dec 1975 [23 Dec 1974] 55518/74 Heading H4F A television system for reproducing separately component pictures from a television signal representing at least two component pictures in the same field, includes for each component picture a display means, switching means for selecting from the television signal the video signals representing the particular component picture, and means, providing a delay less than a field Dean period, to which the signal is applied, the switching means being arranged to select the delayed and undelayed signals in turn so as to increase the field scan rate of the component pictures as displayed by a factor of at least two. The television signal may represent two or more component pictures one above the other in the same field, the received signal being fed through a mixer 31, Fig. 5, to inputs 12, 13 of switches 8B, 8A respectively and also to a delay circuit 10 producing a delay equal to half the field scan period, the direct and delayed signals being shown in Figs. 4(a) and 4(b) respectively. Switches 8A, 8B switch between the direct and delayed signals to pass to displays A, B the waveforms shown in Figs. 4(c) and 4(d) respectively. In a 625 line system, a bistable 19 receives pulses from a circuit 27 every 155 and 311 lines after the beginning of a composite field period to change over the switches. To provide for synchronization in the waveform shown in Fig. 4(d), an AND-gate 33 and a second pulse forming circuit 28 are provided, the output of gate 33 producing a pulse beginning at line 156 in each field, which pulse is fed to mixer 31. Alternatively, the existing pulses 22, 23, Fig. 4(a), could be used for providing synchronization in the B picture output by operating switch 8B after, rather than before, the field synchronizing pulses. The extra vertical sync-pulse may be delayed or advanced by a quarter of a line in addition to the half field delay, so producing a 4:1 interlaced raster. Further, the normal interface may be reduced to 25:75, the extra vertical pulse at the same time being delayed to repeat the delayed lines half a line spacing below their undelayed equivalents. If the camera and display arrangements are modified to provide vertical scanning, vertically split component pictures may be employed. Reference has been directed by the comptroller to Specification 1,438,293.