1. A method for correcting repeated Fixed Pattern Noise (FPN) from a digitally encoded image captured with an image sensor, comprising an array of active pixels arranged in Y rows and M columns, wherein the columns are grouped in subsets of G columns having common blocks readout for reading the pixel image signals, such grouping causing a substantial periodicity in the FPN values, at least one row comprising optically masked pixels which are shielded from incident radiation, so that the output image signals obtained from each at least one optically masked pixel substantially represent FPN of the corresponding column, the method comprising: recording into at least one L-size line memory a value indicative of the FPN values of L optically masked pixels; for each at least one L-size memory, averaging L/N groups of N FPN values from the line memory into a smaller N-size memory, wherein position n t of N-size memory includes a value indicative of the average of every value in position yN+t of L-sized line memory for each integer value of y, wherein 0<=y<=L/N-1 and wherein N is multiple of G; reading the pixel image signals from the array of active pixels; and adjusting the read pixel image signals according to the content of the at least one N-size memory.