$HI,$ I HAVE A QUESTION ABOUT STEP $3.In$ the $eq.of$ Efar$(),$ I don't understand the $apertur{e}^{E(x,y)},$ what does the aperture mean?And I notice $Eois$ outside the integral, I want $to$ ask where $is$ the $h(x)$ and $h(y)$ func. thanks!