METHOD OF AND APPARATUS FOR ENHANCING IMAGE SHARPNESS

An image region including surface roughness or quantized steps is prevented from being sharpness-enhanced. m.times.n pixels around an image signal are extracted, and maximum and minimum value signals Smax, Smin are extracted from the m.times.n pixel data, after which a difference signal Sd (Sd=Smax-Smin) representing the difference between the maximum and minimum value signals Smax, Smin is calculated. If the difference signal Sd is smaller than a threshold th1, then the image signal is judged as being from a region of uniform image density or a region of small density variations, and an enhancement coefficient h is set to h=0. Since an unsharp masking signal h.multidot.k(S-U) is zero, a sharpness-enhanced signal S** is equal to S**=S. Therefore, an image signal free of sharpness enhancement is outputted. Because the image signal from the region of uniform image density is not sharpness-enhanced, a granular state and quantized steps will not be subject to sharpness enhancement.