Image processing method and apparatus for adjusting the tone density of pixels based upon differences between the tone density of a center pixel and tone densities of peripheral pixels

An apparatus for emphasizing an image including a middle tone density area and a binary density area consisting of black and whim picture elements, comprising:

• an image sensor for sensing the image and forming image data consisting of a plurality of pixels each having a tone density;
• storing means for storing said pixels;
• and
• processing means for designating a center pixel and a plurality of peripheral pixels, for determining a sum of differences between the tone density A.sub.0 of said center pixel and the tone density A.sub.i of each of said peripheral pixels, and for adjusting the tone density A.sub.0 of said center pixel based upon a quadratic function of said sum to produce an adjusted tone density A.sub.0 ', such that said processing means edge-sharpens said image in said binary density area without deterioration of the image quality in said middle tone density area.