A method for producing a calibrated radiometric image by un calibrated or partly calibrated thermal imaging device, the method comprising a steps of capturing first and second images on different sets of capturing conditions, obtaining motion matrix characterizing difference between said sets of capturing conditions, obtaining point spread function matrices characterizing a blur condition of said first and second images and obtaining system gain, and calculating a drift by inverting said system gain, motion and point spread function matrices; and calculating a calibrated image by inverting said system gain, motion, point spread function matrices and said first and second images.