Patent US 3,973,239

A pattern preliminary processing system wherein high and low frequency noise other than the pattern signal from a pick-up tube are eliminated by a filtering circuit thereby to "relieve" the pattern against the background and the thus obtained pattern signal is tri-valued into signals of high, medium and low levels by means of a processing circuit having two different threshold values, and then the signal of the medium level is converted into a signal of high or low level with reference to peripheral information thereby to finally bi-value the pattern signal.