1. An image signal processing apparatus, comprising: means for identifying the content of entered image signals; means for storing plural groups of threshold values for binary digitalization of the image signals; means for selecting a suitable group of threshold values in accordance with the identification of the content of entered image signals by said identifying means, and for providing threshold values of the group so selected from said storing means; and means for binary digitalization of said image signals by means of the threshold values provided by said selecting and providing means.