A method of processing an input image produces an output image emphasizing peak-like structures. The input image comprises input pixels and each input pixel has an intensity characteristic. The output image comprises corresponding output pixels and each output pixel has a value. The method comprises the step of calculating for an input pixel the second derivative of the intensity characteristic in two orthogonal directions, one of the directions being the direction of maximum curvature. The product of the two second derivatives is calculated and the value of the output pixel corresponding to the input pixel is determined in dependence on the product.