A method and an apparatus for modifying image forming data including the steps of establishing parameters of an artificial neuronal net during a teaching process on the basis of uncorrected image data and of providing target data based on the original image to be reproduced. The outputs of the neuronal net are utilized for operating an image reproduction device in accordance with data signals modified by the neuronal net on the basis of deviations between the error-free original image and the image to be reproduced.