Patent GB-778183-A (GB)
Title: Improvements relating to the translation of television signals
Inventor: JAMES IVANHOE JOHN PENFOUND
IPC: H04N7/01
Filed: 1953-09-29
Abstract: 778,183. Television. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Sept. 29, 1953, No. 7262/56. Divided out of 778,179. Class 40 (3). In a television system in which an " intermediate image " is produced on the screen of a picture reproducing tube and re-scanned by a picture signal generating tube to produce signals representative of the " intermediate image " but modified in relation to the signals from which this image is produced (e.g. by re-scanning with a repetition frequency different from that employed to reproduce the image) the effect of halation from the picture reproducing tube is reduced by producing the " intermediate image " as a negative picture (in the photographic sense). The modified signals produced by re-scanning are then reversed in polarity to produce conventional signals so that, in images reproduced therefrom, the effects of halation appear in the light parts of the image where they produce a smaller percentage change in light intensity, instead of in the dark parts where such changes in light intensity would be more noticeable. In the described embodiment sequentially developed R (red), G (green) and B (blue) component representative signals, which are produced by means of a camera 1 operating at 150 fields per second and " viewing " the object to be televised through a rotating three-colour R, G, B filter 2, are supplied with suitable polarity, to three picture-reproducing tubes 15, 16, 17 to produce three photographic negative images which are rescanned by respective cameras 5, 6 and 7 operating at a field scanning rate of 50 per second. In order to produce signals suitable for reproduction by both monochrome and colour receivers all of the signals from camera 1 are supplied to tube 15 via a gain-controlled amplifier which modifies the three colour signals such that the signal output of camera 5 is suitable for monochrome reproduction and at the same time constitutes the luminance signal EY which together with colour component signals produced by cameras 6 and 7 forms a composite colour signal of the constant luminance type. To provide these colour component signals tubes 16 and 17 are supplied from the output of camera 1 via gate circuits 13 and 14 which are " opened " (under the control. of signals from a common synchronizing source 3) only during the scanning of the blue and red fields respectively. The signals in the output channels 10, 11 and 12 are then employed for transmission in conventional fashion and may be monitored by a tube 21 operating at 150 frames per second and cooperating with a rotating filter 21 similar to filter 2. In addition to a reduction of halation effects the step of employing a negative intermediate image also reduces line beating effects which occur when the number of lines per field in the tubes 15, 16, 17 differs from the number of lines per field in the cameras 5, 6, 7 (due to enlargement of the spot in the latter cameras in " highlights ") and further reduces the defocusing effect which occurs due to " highlights " in the tubes 15, 16, 17. Reference has been directed by the Comptroller to Specification 719,205.