Image data of an original read by an image reader is analyzed by analyzer means to be supplied to a neural network. An operator inputs scene information and desired finish information to the neural network with data input means.The neural network calculates setup parameter values in compliance with a conversion rule specified by predetermined weighting values and functional forms, and sets these values in an image data converter.Then, the operator corrects the setup parameter values on the basis of finish condition of the produced color separation films. The corrected setup parameter values are inputted to leaning means. The leaning means computes proper weighting values with which the neural network calculates setup parameter values equal to or approximate to the corrected setup parameter values. Such proper weighting values are supplied to the neural network as new weighting values.