1. An adaptive pseudo halftone generator for adaptively converting to a pseudo halftone an input video signal, said signal defining a plurality of sequentially occurring pixels, each having a tone value, and being representative of a binary image and an image with continuous tones, comprising: computing means for computing a contrast value (N) indicative of a degree of continuity of tones of the input image signal by sequentially comparing the tone of an observed pixel with the tones of plural surrounding pixels; threshold preparing means for preparing a threshold value (T) by controlling an amplitude of a periodically varying threshold value on the basis of said contrast value N, said threshold value T being variable with the contrast value N such that as N increases, T approaches a first threshold T.sub.1, which is adapted for binarization of line images and as N decreases, T approaches a second threshold T.sub.2 which is adapted for the binarization of images with halftones; and digitizing means for digitizing the input video signal with respect to the threshold value output from said threshold preparing means to convert the input video signal to a pseudo halftone.