in a picture image enlarging / reducing system of the type wherein image magnification by a desired factor is achieved by first enlarging the image by an integer factor greater than the desired factor and then multiplying the enlarged image by a correction coefficient corresponding to the ratio of the desired factor to the integer factor , a zero judging circuit is provided to detect whether a line or a part of a line in the picture image is all zeros . if so , the zeros are inserted into the magnified picture image signal directly in accordance with the desired magnification factor .