Patent GB-1338653-A (GB)
Title: Adaptive multiple speed facsimile system
IPC: H04N1/17
Filed: 1971-04-19
Abstract: 1338653 Facsimile apparatus COMFAX COMMUNICATIONS INDUSTRIES Inc 19 April 1971 [24 March 1970] 25140/71 Heading H4F Image data obtained from an original document is transmitted to a receiving station for facsimile reproduction at either a fast or a slow rate of transmission, depending on the content of the part of the image being transmitted. Preferably scanning of both the original document and the copy is similarly effected at one of two different speeds. In this way due time is taken over the scanning and image data transmission of parts of the document containing image details, while a minimum of time is spent over parts of the image which contain no information. Transmitter.-Fig. 3 shows transmission apparatus including a reading head 82, a reading logic section 84 and a telephone line interface 34. In the reading head 82 a document 10 is scanned by a C.R.T. 20 and the output from a photomultiplier 26 is converted to a two-level image signal corresponding to black and white on the document 10 by means of a comparator 106. The image data is conditioned in a conditioner 108 so that it emerges on line 114 as a two-level series of signal elements each corresponding in duration to the spot size of the C.R.T. 20. The conditioned signal is applied to a circuit 116, where its image content is analysed to determine at which rate it is to be transmitted through a shift register 118 to the interface 34. The circuit 116 controls the rates of transmission and scanning by supplying an appropriate clock signal on line 126 to the register 118 and also to sweep generator 128. if the image signal represents thirty-two consecutive signal elements representing white on the document 10, the transmission and scanning rate is switched from slow to fast, returning again to the slow rate as soon as the next black element occurs. End of line scan signals generated by the sweep generator 128 and begin line scan enable signals from a circuit 138 are used to ensure that each new line of scanning begins at the fast rate. A signal on line 148 indicating whether scanning and transmission is at the fast or the slow rate is combined at 30 within the interface 34 with the black/white data on line 146, a start/stop signal on line 144 and a synchronization code on line 150 to produce a three-line signal containing all this information for transmission. In a modification in which a two-level signal is transmitted the fast/slow instruction is incorporated as a unique code, any image signal portions which duplicate this code being modified for transmission purposes and reconverted to their original form only after extraction of the rate information code in the receiver. Receiver.-Fig. 4 illustrates the receiving apparatus, in which the fast/slow information is extracted by a fast/slow decision circuit 270 and applied to the sweep generator 282 of the reproducing C.R.T. 48. Stepping of a motor 72 to move the copy 50 by a lines-width is likewise synchronized with the corresponding motor 38, Fig. 3a, in the transmitter. The white/black signal data is extracted in a detector 272 and supplied to the C.R.T. 48 via an unblanking circuit 298. Start/stop and line begin/end instructions are similarly extracted and used. A signal is sent back from the receiver to the transmitter on line 168, Fig. 3, to signify when a copy sheet is in position.