A method and an apparatus for determining near field images for optical lithography include receiving a thin mask image indicative of a photomask feature, in which the thin mask image is determined without considering a mask topography effect associated with the photomask feature, and determining a near field image from the thin mask image by a processor using an artificial neural network (ANN), in which the ANN uses the thin mask image as input. The apparatus includes a processor and a memory coupled to the processor. The memory configured to store instructions executed by the processor to perform the method.