In an image processing method for obtaining a processed image signal from an original image signal representing an original image having a certain picture element density, a plurality of intermediate image signals which are different in frequency band are made on the basis of the original image signal. A plurality of transformed image signals are obtained by carrying out a transformation processing on the respective intermediate image signals on the basis of respective transformation functions, and a processed image signal is obtained from the transformed image signals. The transformation functions are defined by determining transformation function defining parameters for the transformation functions on the basis of the picture element density of the original image.