Patent GB-495740-A (GB)
Title: Improvements in or relating to image transmission systems
IPC: G08C21/00
Filed: 1937-12-22
Abstract: 495,740. Electric signalling systems. ELECTRICAL RESEARCH PRODUCTS, Inc. Dec. 22, 1937, No. 35498. Convention date, Dec. 24, 1936. [Class 40 (i)] [Also in Group XXXIX] In a writing telegraph system, the two co-ordinate potentials derived by tracing a cartoon, outlines of areas of a picture &c., instead of being directly transmitted as usual, are first recorded so that by transmission at a speed within the requirements of persistence of vision, and using the received signals to control the potentials on deflector plates of a cathode-ray tube, a complete image of the subject traced may be viewed. The record is repeatedly transmitted, or a series of varying records may be used to provide moving images at the receiver. In one arrangement the record is transmitted during the tracing so that a gradually built up image is viewed. A sound accompaniment may also be recorded. The transmission may be by modulated carriers over a line or by radio and the band width required for good definition being approximately 14000#, the sound channel being placed between the two image channels which comprise single side bands with their carriers adjacent the sound channel. Specification 288,234, [Class 40 (iii)], is referred to. In the system shown in Figs. 1, 3 and 4, the recording arrangement, Fig. 1, comprises a stylus 10 which during movement over distinctive areas of the subject O taps off variable potentials from potentiometers 11, 12 which are fed to light valves 28, 29 and recorded as variable density or area tracks 36, 42 on a film 35. A sound accompaniment from microphone 44 may be recorded on track 43 and track 51 records periods in which the stylus is raised out of contact with the subject. As, however, the image tracks 36, 42 are recorded at a slower speed than subsequent reproduction, the sound may be recorded at the speed of transmission on a separate film and then transferred to the image film. A stylus controlled frame, Fig. 2 (not shown), is described for effecting the co-ordinate movements of the potentiometer sliders, and the stylus, Fig. 7 (not shown), has a spring-controlled movable rod for closing the circuit of magnets 65 controlling light valve 69 when the stylus is actually tracing the subject, to make the record track 51. An alternative method consists in moving the stylus so quickly when not in contact with the subject so that reproduction of such movement is very faint. The record formed into an endless band is then passed through a photo-electric transmitter, Fig. 3, the light passing through each track activating a separate cell 77-80 the outputs of which modulate separate carriers, the modulated signals after amplification being transmitted over line 94 or by wireless. At the receiver, Fig. 4, the four sets of signals are separated by filters and demodulated, the two sets of co-ordinate signals from 100, 101 being impressed on deflecting plates 104, 105 of a cathode-ray tube, so that the movements of the spot provide an image of the subject. The output of demodulator 102 consisting of signals indicating when the stylus was lifted from the subject, is applied to electrode 111 to cut off the ray at corresponding periods. The sound channel from demodulator 103 is reproduced in the usual manner. A modification, Fig. 8 (not shown), utilizes a disc record with circular tracks of variable area or density. Moving pictures, Fig. 10. A film, e.g. comprising an animated cartoon is projected frame by frame from 230 on a ground glass screen 231 and traced by a stylus 232 which is connected by cords 235, 236 to spring-controlled slides 239, 240 of a pair of light valves for making a pair of variable area or density record tracks. The connection between the stylus and light valves may be electrical, and a track indicating when the stylus is in contact with the screen may be recorded. Also, a magnetic tape or wax or metal record may be used with appropriate recording instruments. The density of reproduced lines depends on the speed of the stylus. In cases where a series of frames have the same background picture, tracing is facilitated by providing a grooved template 261, Fig. 11, for the background. Modification, Fig. 14, in which the building up of the received image is viewed by transmitting each element immediately after recording. A combined transmitter and recorder comprises a drum 336 making 20 revolutions per second and carrying a record strip 337 on a transparent circumferential portion 338. The recording instruments comprise magnets 319, 320 and cutters 317, 318 mounted on an arm 321 driven by gearing 332-335 so that it rotates slightly faster than the drum and makes a complete revolution relative thereto in the time required for tracing the subject, the leads to the magnets being taken through brushes and slip rings. The record film 337 has an opaque coating in which variable area tracks are made by the cutters, but other types of record and recording instruments may be used. The two light sources and optical systems are mounted within screens inside the drum and transmission is effected as previously described.