Patent GB-1386283-A (GB)
Title: Television message transmission system
IPC: H04N1/64
Filed: 1972-04-27
Abstract: 1386283 Television INTERNATIONAL STANDARD ELECTRIC CORP 27 April 1972 [27 April 1971] 19623/72 Heading H4F For the transmission of auxiliary pictures during the field-blanking intervals in a standdard TV signal the auxiliary subject (e.g. picture, text or static or slowly changing threedimensional scene) is scanned using a raster having simultaneous electronic slip of both the vertical and horizontal scanning frequencies relative to the raster of the standard TV signal. Thus, for example, in a 625 line per frame TV system a fascimile original may be scanned using a shorter line duration such that 625 standard lines occupy the same period as 626 fascimile lines. If the facsmile signal BASF is gated at the same line of the standard TV scan during the field blanking intervals of successive TV frames and the gated lines are added to the standard TV signals FBAS for transmission, the complete 625 lines of the facsimile scan can be transmitted during 625 standard TV frames. The slip may be greater than 1 and may be positive or negative. Facsimile tranmission can be completed more rapidly by gating several facsimile lines into each field blanking interval. Moreover, subfacsimile signals can be inserted into such lines of the facsimile signals as would not otherwise carry information, using either the same technique or other methods involving mechanical movement of an original to provide vertical scanning. Transmitter.-Synchronizing and gating signals for the facsimile system are derived from the standard TV sync. signal S (Fig. 3). This is converted to a signal of frequency f H  (line frequency of the standard raster) in S-to-H converter 5, which is divided by 625 in divider 6 to provide a 25 Hz signal and this frequency is added to f H  at 7 to form a signal with frequency f H <SP>1</SP> (line frequency of the facsimile raster). The frequency is doubled at 8 and supplied to pulse generator 9 which produces facsimile sync. signal S F  as well as horizontal, vertical and blanking signals H F , V F  and A F . Phase ambiguity of S F  is prevented by comparing the phases of S F  and f H <SP>1</SP>. Grating pulse T F  is derived from S by line selector 10. To ensure synchronism between S F  and T F  the latter is compared with the 25 Hz output of divider 6 in coincidence stage 10a and the output signal disturbs the division ratio until phase coincidence exists. Receiver (Fig. 4).-The incoming signal is gated at 11, to obtain the facsimile line from each standard TV frame, and is passed to reproducer 12 including a TV picture tube or a short persistence tube as used in slide and film scanners. The modulated light spot is imaged on photosensitive layer 14 on which the complete facsimile image is eventually built up. Deflection of the light spot, which may alternatively be produced by a laser, is effected by deflection unit 15 operated with S F  or H F , V F  and A F . Vertical deflection may take place stepwise or at a slow rate corresponding to the facsimile line sequence. Preferably deflection corresponds to that of the pick up unit in the transmitter (625 lines per frame, 50 fields per second). S F  and T F  are derived from the transmitted sync. signal S in a circuit similar to that shown in Fig. 3. After production of facsimile line frequency signal f H <SP>1</SP>, which signal is extracted as H F , this signal is divided by 625 and multiplied by two to provide signal VF. Sync. signal S F  is derived from H F  and V F . To synchronize the transmitted and received signals vertically pulses T F  and S F  in the transmitter can be compared in phase and a comparison signal transmitted. This signal is compared with the comparison signal from S F  and T F  in the receiver and the phase of V F  is corrected accordingly. Colour reproduction. - When transmitting NTSC or PAL signals the single colour burst per frame in the facsimile receiver is insufficient to regenerate the colour carrier. Gate 11 (Fig. 4) is therefore followed by a colour carrier regenerator 25 capable of responding to the received burst. Device 26 forms from the regenerated carrier and sync. signal S F  a burst sequence which then forms in device 27, with gated facsimile signal FAX-S and sync. signal S F , a facsimile FBAS signal which can be converted by a normal colour decoder into a facsimile colour TV picture. With PAL, SECAM (Registered Trade Mark), SECAM-IV and ART systems at least two sequential facsimile lines are transmitted per frame or per field. In the SECAM system the necessary storage of sequential lines can be achieved by the photosensitive layer 14. In the FAM system the demodulated signal R-Y must be gated with the gating pulse T F . Episcope operation.-In an alternative method of transmitting colour pictures the pick-up at the transmitter produces signals R - Y, B - Y and Y. With R - Y and B - Y or I and Q, or other combinations of R, G and B, or with R, G and B, two colour carriers are amplitude modulated or frequency modulated or one carrier is amplitude modulated and the other frequency modulated, or one is FAM-modulated, or one is NTSC modulated. The NTSC carrier additionally contains a pilot carrier. The selected carriers are added to the luminance signal. In the receiver the reproduced image is recorded on a carrier 14 capable of recording black-and-white and half tones only (Fig. 6). During episcope operation an unmodulated raster is imaged on the carrier and reflected light is picked up by photocells 25, 26, 27, if a coloured image is present on 14, or by a single photocell if a black-and-white image with coded colour is present. A colour signal suitable for reproduction in a colour TV receiver is then formed at 28, preferably modulated on an RF carrier at 29. For episcope operation an internal sync. signal is generated by an oscillator which produces a signal at line frequency from which sync. signal S F <SP>1</SP> is derived. In a modified recording arrangement the luninance and colour information signals are recorded on separate successive frames of carrier 14. For reproduction the sanning spot is divided into two. Recording medium.-Recording medium 14 may be normal film, Polaroid (Registered Trade Mark) film or sensitized paper. Alternatively a tape recorder or magnetic disc may be used. In the latter case one line is preferably recorded during each revolution of the disc. If recording has to be effected slowly each incoming line can be stored and then fed to the recording equipment during the interval before the next line arrives. Applications.-The system may be used to transmit information about the transmitting station, stockmarket prices, weather charts, current forecasts based on incoming election results, departure times at airports or information for data processing. Electronic test patterns, marker pulses and alphanumeric characters from a character generator may also be transmitted. Photographing television pictures.-The facsimile reproducing equipment of Fig. 4 may be used to photograph single television pictures if provided with electronic equipment for keying and control. Written pages.-Reproduction of size DIN A4 pages can be improved by transmitting the upper and lower halves in successive frames. Modifications.-Instead of the processing circuit of Fig. 3 for deriving facsimile sync. signal S F  highly stabilized generators may be used to generate S and S F . Sync. signals at the receiver may be generated similarly.