1. A noise filtering method implemented using a computer for enhancing images, said method comprising the steps of: calculating a magnitude E.sub.i of density change for each of a plurality of linear direction components i in a local region around each pixel of an input image; and conducting one-dimensional smoothing processing for each pixel of the input image in a linear direction of one of said plurality of linear direction components, said linear direction for each pixel being selected on a basis of having a minimum said magnitude E.sub.i of density change for that pixel as calculated in said calculating step.