Patent GB-1412798-A (GB)
Title: Facsimile system
IPC: H04N1/17
Filed: 1972-10-17
Abstract: 1412798 Copying by scanning MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 17 Oct 1972 [18 Oct 1971 24 Nov 1971] 47812/72 Heading H4F Bandwidth reduction of a facsimile signal is accomplished by transmitting only those portions of the signal which relate to divisions of a scanned original (divisions of the scanned lines or area divisions of the original) which contain picture information, i.e. black marks, the resulting signal portions, which are in digital form, being frequency converted before transmission by being written into a shift register at one rate and subseqeuntly read out at a slower rate, a synchronizing signal being associated with each such frequency converted signal portion to control the operation of the receiver to reconstitute the original signal using a shift register to frequency convert the signals to their original frequency. In one embodiment, Fig. 3a (also Figs, 1, 2, 5, and 6, not shown) each scanned line is regarded as being split into 32 divisions, the portion of the signal, of duration d, due to the first division d1 being gated and read into the transmitter shift register as it is derived, a, the synchronizin g signal for this division being transmitted in the following period, b, of duration 4d, and this first picture signal portion being then read out of the shift register at 1/32 the frequency with which it was written in, and transmitted, c. Due to a blanking period of 4d the picture signal portion which is gated and read into the transmitter shift register when the first portion has been transmitted is that representing the second division d2, as the same line of the original has been rescanned. As the divisions d2-d5 contain no picture information, the next processed signal portion represents division d6, periods f, g and h for division d, corresponding to periods a, b, and c for division d1. When all the signal portions for one line which contain information have been transmitted, the scanning is advanced to the next line. Each synchronizing signal may be split into two parts b<1>, b<11>, Fig. 3b, of lengths 3d and d respectively. In an alternative embodiment, Fig. 8, each picture signal portion is read out of the transmitter shift register in a period equal to two line scans, rather than one line scan as previously. In either of these embodiments the synchronizing signals may be transmitted as amplitude modulation of a carrier, the picture signal being transmitted as either amplitude or frequency modulation of a carrier. In a further embodiment, Fig. 21 (also Figs. 17-20, not shown), the synchronization signals for all the divisions in one line scan containing picture information are memorized in a separate shift register at the transmitter, S703' these signals then being non-destructively read out in a period equal to two line scans, and transmitted to the receiver, S704, where they are memorized in a further shift register, the thus memorized signals in the transmitter and receiver being simultaneously read out and used to control the timing of the write in of the picture signals into their respective picture signal shift registers, the picture signals for one line being transmitted before further synchronizing signals (for the next line) are transmitted. In this last embodiment, the synchronizing signals for each line may alternatively be made of two lines duration by changing the scanning so that the synchronizing signals are derived during a line scan of twice the normal duration. Alternatively the synchronizing signals for each line may be transmitted as derived, i.e. of one line duration (Figs. 13-16, not shown). The scanned original may alternatively be regarded as formed of a plurality of square area divisions, Fig. 23, each having the same information capacity ias the line division I previously used, and each being scanned in a plurality of lines (Figs. 24-26, not shown). The frequency conversion factor may be varied according to the quantity of picture information in the divisions.