Optical proximity correction (OPC) based computational lithography techniques are disclosed herein for enhancing lithography printability. An exemplary mask optimization method includes receiving an integrated circuit (IC) design layout having an IC pattern; generating target points for a contour corresponding with the IC pattern based on a target placement model, wherein the target placement model is selected based on a classification of the IC pattern; and performing an OPC on the IC pattern using the target points, thereby generating a modified IC design layout. The method can further include fabricating a mask based on the modified IC design layout. The OPC can select an OPC model based on the classification of the IC pattern. The OPC model can weight the target placement model.