Method and apparatus for electrically transmitting pictures

Claim 1

In apparatus for electrically transmitting pictures containing black, white and gray brightness values by effecting at the transmitting end, a line-by-line photoelectric scanning of the picture to be transmitted to produce a scanning voltage proportional to the brightness value at each scanning instant, and controlling at the receiving end, a device for reproducing the picture, which device is capable of reproducing only a black or white brightness value at any given instant, the improvement comprising: means for quantizing the amplitudes of the scanning voltage, at the transmitting end, at successive intervals into a white range containing the low voltage amplitudes, a black range containing the high voltage amplitudes, and at least one gray range disposed between the white range and the black range and containing the medium voltage amplitudes corresponding to the gray values of the picture to be transmitted; means for producing a signal identifying the particular range existing during each interval means for; transmitting each signal to the receiving end; and, at the receiver end: evaluator means connected for receiving the transmitted signals and deriving from each such signal a direct voltage value representative of the value of such signal; a plurality of pulse generators connected to said evaluator means and each response to only one direct voltage value corresponding to a respective gray range for producing a particular pulse sequence each time such direct voltage value is received, the ratio of pulse duration to pulse interval of the sequence produced by each said generator being proportional to the amplitude of the scanning voltages in the range corresponding to the direcT voltage to which it is responsive; switching means connected to said evaluator means for producing a first direct voltage when the direct voltage produced by said evaluator means corresponds to the white range scanned voltages and for producing a second direct voltage when the direct voltage produced by said evaluator means corresponds to the black range scanned voltages; and means connecting the outputs of said pulse generators and said switching means to the picture reproducing device.