GB1022472A - Improvements in and relating to television standards converters - Google Patents

Abstract

1,022,472. Television. BRITISH BROADCASTING CORPORATION. May 15, 1963 [July 20, 19621, No. 28036/62. Heading H4F. Television signals representative of pictures made up of two or more interlaced fields are converted to signals of a different line repetition frequency by forming an intermediate raster " display " which is scanned off at the different line frequency, the arrangement being characterized by means for " displaying " substantially simultaneously signals from fields recurring successively in the input signal. The term " display " embraces both visible displays and invisible electrostatic records in cathode-ray storage tubes. In a first arrangement, Fig. 1, input signals representative of pictures each made up of two interlaced fields are applied directly to a cathode-ray display tube 10 and via a delay unit 11 having a delay equal to the duration of one field plus (or minus) half one line to a second display tube 12. The tubes are scanned in conventional interlaced rasters under the control of the synchronizing signals with the input signals and their displays are combined by half silvered mirror 13 and scanned off at a different line repetition frequency by a camera 15. Tubes 10 and 12 display simultaneously successively occurring input fields (so producing a composite display comprising a complete picture) and to ensure convect line interlacing one or other image is shifted vertically through an appropriate distance, the direction of shift depending on which image is shifted and whether the delay in unit 11 has a duration of one field plus or minus half a line. A spot-wobble oscillator 16 applies spot wobble to both tubes, the amplitude of the wobble being made equal to half the spacing between adjacent picture lines assuming the spot wobble to be triangular. If a sinusoidal wobble is employed the amplitude is made equal to # of the picture line spacing. The scanning of tube 12 may be synchronized by the synchronizing pulses in the delayed signal in the output of unit 11. In this arrangement the delay of unit 11 may have any value approximating to the duration of one input field. In a second arrangement, Fig. 3, only a single cathode-ray tube 17 is employed to which the direct and delayed signals 1 and 2 are applied alternately, at a frequency high compared with the line frequency, by means of a sampling switch 18 controlled by an oscillator 19 which also applies spot wobble to the tube. The amplitude of the wobble is equal to half the spacing between field lines (assuming a triangular wobble) and the phase of the switch operation is such that signal 1, say, is displayed on the top half of each cycle of wobble waveform as shown in Fig. 4 in solid lines, whilst signal 2 is displayed on the bottom half of each cycle as shown in dotted lines. The composite display comprising a complete picture is scanned off at the different line frequency by camera 20. Vertical aperture correction to compensate for picture distortion due to information in one line being modified by information due to the two adjacent lines may be introduced by the arrangement shown in Fig. 5. The original signal 1<SP>1</SP> due to one field has subtracted from it in stage 21 a proportion (determined by attenuator 30) of signals 21 and 211 due to the adjacent lines in the next preceding field obtained by delaying the input signals in units 23 and 25 and combining the delayed signals in adder 24. Similarly the signal 2<SP>11</SP> due to the delayed field has subtracted from it in stage 32 a proportion K of the signals 1<SP>1</SP> and 1<SP>11</SP> due to the adjacent lines in the next succeeding field which are derived respectively from the input signal directly and the input signal delayed in unit 22. The signals are added in adder 28 and applied to stage 32 via attenuator 31. The signals appearing at terminals 3 and 4 are substituted for signals 1 and 2 in Figs. 1 and 3. A modified arrangement, Fig. 7 (not shown), is arranged so that both the direct and delayed field signals are corrected by signals from the preceding field. This arrangement is stated to permit correction for the effects of cathode-ray tube afterglow.