A method and system for computing Fourier coefficients for a Fourier representation of a mask transmission function for a lithography mask. The method includes: sampling a polygon of a mask pattern of the lithography mask to obtain an indicator function which defines the polygon, performing a Fourier Transform on the indicator function to obtain preliminary Fourier coefficients, and scaling the Fourier coefficients for the Fourier representation of the mask transmission function, where at least one of the steps is carried out using a computer device.