▁the ▁Gaussian ▁function ▁is ▁both ▁separ able ▁and ▁is otrop ic . ▁The ▁separ able ▁forms ▁of ▁all ▁other ▁window ▁functions ▁have ▁corners ▁that ▁depend ▁on ▁the ▁choice ▁of ▁the ▁coordinate ▁axes . ▁The ▁is ot ropy / an is ot ropy ▁of ▁a ▁two - dimensional ▁window ▁function ▁is ▁shared ▁by ▁its ▁two - dimensional ▁Fourier ▁transform . ▁The ▁difference ▁between ▁the ▁separ able ▁and ▁radial ▁forms ▁is ▁a kin ▁to ▁the ▁result ▁of ▁diff raction ▁from ▁rect angular ▁vs . ▁circular ▁app ert ures , ▁which ▁can ▁be ▁visual ized ▁in ▁terms ▁of ▁the ▁product ▁of ▁two ▁s inc ▁functions ▁vs . ▁an ▁Air y ▁function , ▁respectively . ▁ ▁See ▁also ▁▁▁ ▁Spect ral ▁leak age ▁ ▁Mult it aper ▁ ▁Ap od ization ▁ ▁Wel ch ▁method ▁ ▁Short - time ▁Fourier ▁transform ▁ ▁Window ▁design ▁method ▁ ▁Kol m og or ov – Z ur ben ko ▁filter ▁ ▁Notes ▁ ▁Page ▁cit ations ▁ ▁References ▁ ▁Further ▁reading ▁ ▁External ▁links ▁ ▁Lab View ▁Help , ▁Character istics ▁of ▁Sm o othing ▁Fil ters , ▁http :// zone . ni . com / reference / en - XX / help / 3 7 1 3 6 1 B - 0 1 / l van ls con cept s / char _ sm o othing _ windows / ▁ ▁E valu ation ▁of ▁Vari ous ▁Window ▁Function ▁using ▁Multi - Inst rument , ▁http :// www . multi - inst rument . com / doc / D 1