1. A method for signal conditioning of signals from a two-dimensional image, the method comprising: calculating the motion of the image in relation to an image plane, correlating the images that are separated in time using Radon transforms calculated all over the image for at least two angles in order to reduce a two-dimensional correlation problem to correlation of at least two one-dimensional projections, and differentiating the one-dimensional projections in order to obtain the gradients of the projections as the basis for the correlation of images separated in time and signal conditioning, wherein the correlation of images separated in time is carried out independent of the absolute signal strength for the different part of a scene based upon the gradients of the projections.