by an actual cdf s 10 of each frame to be corrected all cdfs are computed by a cdf generator cdfg which receives signal s 2 frames restricted to region for detection and correction further restricted to set of pixels for detection hence if the set of pixels for detection is not the whole frame or frame region both cdfs may be based on sub sampled data although the correction step is applied to each entire frame or frame region which is computationally economical the correction process carried out by the corrector corr has been described in detail in the summary section the actual value x curr of the image component in a pixel is replaced by the corrected value x corr which is that admissible value which minimises f x curr u2212 f ref x corr where f is the cdf of the frame and f ref is the reference cdf which is generated on the basis of cdfs of earlier frames the process is visualised by fig3 the sub steps being shown by the sequence of arrows for the exemplary actual pixel value 139 1 the actual cdf f is read for the pixel value 139 and its cumulated probability the probability of picking a pixel having a value u2266 139 is found to be 0 50 2 the point on the reference cdf f ref having this cumulated probability is retrieved and 3 the corresponding pixel value 113 is the corrected value with which the actual pixel value is replaced in connection with this exemplary embodiment.