1. A method of filtering noise of low frequency from an image of surface characteristics of an object expressed with reference to orthogonal first and second axis and obtained with linear light scanning of said object along said first axis, comprising the steps of: i) calculating a difference between pixel values of an image column vector along said second axis adjacent a selected reference image column vector and respective pixel values of said selected reference image column vector to obtain a pixel difference vector; ii) selecting the pixel difference values not mainly associated with a corresponding atypical change of surface characteristics as compared with noise; iii) calculating a mean value from said selected pixel difference values as an estimated value of said noise; iv) subtracting the estimated noise value from the adjacent image column vector to obtain a corrected image column vector; v) repeating said steps i) to iv) using the corrected image vector as said reference image column vector and a further adjacent image column vector to obtain further corrected image column vectors; and vi) generating a noise filtered image from the obtained corrected image column vectors.