PURPOSE: To emphasize a white level and a black level, and to emphasize a contour, by executing quantization separately from other parts with respect to an address of a coordinate positioned in the center part of a dither matirx.

CONSTITUTION: An input analog signal is quantized by an A/D converter 11, is compared with a threshold signal of a picture element corresponding to an address signal outputted from an ROM9 for dither matrix and a dithered picture signal is outputted. When an address signal of a coordinate positioned in the center part of a dither matrix is generated, a picture signal compensating circuit 6 is operated and the input analog signal is emphasized in the direction of a white level or a black level. Accordingly, a quantized signal of an analog picture signal whose black level and white level are emphasized is compared with a threshold level quantized signal.