1. A method for processing a two-dimensional initial image used in a medical procedure, comprising: dismantling the two-dimensional initial image into a plurality of partial images and a residual image by a computer, wherein each of the partial images contains a component of the two-dimensional initial image that varies locally with a predetermined partial image frequency departing from zero, wherein the residual image contains a direct component of the two-dimensional initial image that is locally invariable; assigning one of the partial images as a pilot image and assigning a frequency of the pilot image as a pilot frequency based on a comparison of frequencies of the partial images with a target frequency; determining a plurality of weighting factors for the partial images and the residual image; and summing the weighted partial images and the weighted residual image into a final image, wherein the weighting factors of the partial images are determined by the computer so that: the partial images with lower frequencies than the pilot frequency are weighted less than the pilot image but still contribute to the final image, the partial images with higher frequencies above the pilot make: a large contribution to the final image when a noise component in the initial image is small, or a small contribution to the final image when the noise component in the initial image is large.