GB813510A - Improvements in and relating to the compression of band-width of television signals - Google Patents

Abstract

813,510. Television. BRITISH BROADCASTING CORPORATION. Dec. 6, 1956 [Dec. 16, 1955], No. 36216/55. Class 40 (3). [Also in Group XXXIX] In a quantizing arrangement for a television signal the number of amplitude levels available in the quantizer is varied inversely as the number of significant amplitude changes in the television signal in a given time interval. This allows a better use of the bandwidth available for transmission when the television signal contains only components of relatively low frequency. As shown in Fig. 1, the signals to be quantized are supplied from terminal 10, to a first quantizer 15 which has the maximum number of levels which are ever required and the output signals supplied, during alternate line periods, via switch 16, to counters 17, 18, the outputs from which, consisting of a potential of amplitude proportional to the number of amplitude changes in one line of the signal from 15, are supplied during the other alternate line periods, via switch 19, to a second quantizer 20 to control the level at which quanta are produced in inverse ratio to the amplitude of the applied control signal, the signals from terminal 10 being also supplied to quantizer 20, either via a delay device introducing a delay of one line period or, as shown, from alternate ones of storage devices 12, 13 during the other alternate line periods. The output from quantizer 20 is utilized in similar manner to the output of the quantizer 13 of Specification 795,193 to produce trains of pulses for transmission by supplying such output firstly, to a generator 21 which supplies pulses of amplitude proportional to the amplitude of the quantized signal via switches 22 and 25 and storage devices 23, 24 operative respectively during alternate line periods to an output terminal 26 and, secondly, to a generator 31, which supplies pulses indicative of the position of each quantum in each line, via switches 32 and 35 and storage devices 33, 34 operative respectively during alternate line periods, to an output terminal 36 .the generator 31 also controlling the " writing " and " reading " time bases 28, 30 respectively of the storage devices. The Specification includes a description of the quantizer 20 with reference to Fig. 4 (not shown), which is identical with that described in Specification 781,325 (see Group XXXIX) with the exception that the control voltage applied to the cathodes of the double diode 24 from the manually adjustable potentiometer 26 in Fig. 2 of the latter application is, in the present invention, supplied from switch 19. Suitable arrangements for the counter circuits 17, 18 and for the generators 21, 31 are described with reference to Figs. 2 and 3 (not shown) and Fig. 5 (not shown) respectively.