Pulse code modulation with few amplitude steps

Claim 1

APPARATUS FOR TELEVISION TRANSMISSION INCLUDING, IN COMBINATION, A TRANSMITTER HAVING A SIGNAL SOURCE TO SCAN A PICTURE HAVING AREAS OF VARIABLE LIGHTNESS BY TRACING A RASTER OF LINES THEREON TO PRODUCE A FIRST SIGNAL VARYING IN AMPLITUDE AS A FUNCTION OF SAID VARIABLE LIGHTNESS, MEANS TO PRODUCE CLOCK PULSES REPEATING AT A RATE EQUAL TO THE RATE OF TRACING CLOSELY SPACED POINTS TO BE SAMPLED IN EACH LINE, A FIRST PSEUDO-RANDOM STEP FUNCTION GENERATOR ADVANCED SEQUENTIALLY BY THE CLOCK PULSE TO PRODUCE A SECOND SIGNAL HAVING A STEP PATTERN REPEATING ONLY AFTER A SUBSTANTIAL NUMBER OF LINES, MEANS TO PRODUCE A THIRD SIGNAL HAVING AN AMPLITUDE VARYING AS THE SUM OF THE AMPLITUDES OF THE FIRST AND SECOND SIGNALS, A QUANTIZER ACTUATED BY THE CLOCK PULSES TO SAMPLE THE THIRD SIGNAL AND TO CLASSIFY EACH SAMPLE AS FALLING WITHIN A PARTICULAR ONE OF A PLURALITY OF OF AMPLITUDE STEPS, AND PULSE CODE TRANSMISSION MEANS FOR THE CLOCK PULSES AND THE OUTPUT OF THE QUANTIZER, AND A RECEIVER HAVING A DIGITAL-TO-ANALOG CONVERTER FOR THE OUTPUT OF THE TRANSMITTER, A SECOND PSEUDO-RANDOM STEP FUNCTION GENERATOR ADVANCED SEQUENTIALLY BY THE TRANSMITTED CLOCK PULSES TO PRODUCE A FOURTH SIGNAL IDENTICAL TO THE SECOND SIGNAL, AND MEANS TO PRODUCE A RESULTING SIGNAL HAVING AN AMPLITUDE VARYING AS THE DIFFERENCE BETWEEN THE AMPLITUDES OF THE CONVERTER OUTPUT AND THE FOURTH SIGNAL.