Patent GB-526585-A (GB)
Title: Improvements in or relating to facsimile transmission systems
IPC: H04N1/50
Filed: 1939-03-21
Abstract: 526,585. Facsimile transmission system. STANDARD TELEPHONES & CABLES, Ltd. (Finch, W. G. H.). March 21, 1939, No. 8954. [Class 40 (iii)] A method of transmitting coloured pictures comprises scanning the original picture a plurality of times with overlapping scanning, or alternatively scanning as one complete picture a set of colour separation prints derived from the original picture, to produce electrical signals varying in intensity in accordance with colour components of the picture and translating the signals into colour separation prints at the receiver. In one embodiment a coloured picture is resolved by photographic processes into three monochrome colour separation prints B, R, Y, Fig. 1, which are fixed on a sheet 1. This sheet is mounted on the drum 6, Fig. 2, of the transmitter 7 where it is scanned by an electro-optical scanner 12, both drum and scanner being driven from a synchronous motor 8. The resulting signals are transmitted over a telephone circuit 17, 18, 23, 25 and 27 to the receiving scanner 28, Fig. 3, which projects varying light intensities to a light-sensitive sheet 29. The receiver is driven in synchronism with the transmitter by motor 31. The facsimile reproduction may also be performed with varying line width, varying line density, or by dot-dash methods. The film 29 is developed and bleached, the different prints then being separately dyed or toned to their original colour. Finally they are superimposed to form the final picture, Fig. 6, or they may be used for colour -photoengraving. Since the three prints B, R, Y of the original were scanned vertically, the scanning lines of R1 and Y1, Fig. 6, are displaced onethird and two-thirds of a line width respectively from the lines of B<SP>1</SP>, the effect being to treble the number of scanning lines. In a second embodiment, Fig. 8, the original coloured picture is mounted on a transmitter drum 6 which is driven at 100 r.p.m. The scanner 12 is driven at onethird of an inch per minute, and a beam onehundredth of an inch wide from a source 44 is reflected from the picture 1 through a colour filter 50 rotating at 33 1/3rd r.p.m. to the photoelectric cell 49. The filter 50, which is driven by the flexible drive 51, contains three sectors, each occupying 120‹, so that light of a different colour passes to the cell 49 each revolution of the drum 6. The scanner moves one three-hundredth of an inch for each revolution of the drum so that the picture is effectively scanned with overlapping lines three times, once for each colcur component. By choice of the colour filters either positives or negatives may be produced. At the receiver, a synchronously driven cam 93, Fig. 12, closes switches 95, 94, 96 to connect the received impulses in turn to scanners 67, 68, 66. The receiver is driven synchronously with the transmitter, each scanner having beams one-hundredth of an inch wide so that, each being operated in turn, they produce the three colour separation prints R, B, Y. To adapt the transmitter for monochrome picture transmission, a changespeed-gear may be inserted in the drive shaft 40, Fig. 8, to vary the speed of the scanner 12, and the filter disc is removed. In a further embodiment Fig. 15 (not shown) a receiver, adaptable for either colour or monochrome reproduction, has change-speed gear in the drive from its motor. For colour reception the diameter of the drum of the receiver is made three times ttat of the transmitter and is rotated at 33 1/3rd r.p.m., the scanner being moved at one-third of an inch per minute and having a beam one-hundredth of an inch wide. For monochrome reception the diameters of transmitter and receiver drums are equal.