A method of generating a mask is provided that optimizes the placement and shape of optical proximity correction (OPC) features such as scattering bars. According to some aspects, the method includes model-based techniques for determining where to place assist features within the design, thereby eliminating the need for experienced mask designers to perform OPC, and also substantially reducing the time required to determine an acceptable OPC solution. According to further aspects, the method provides an OPC assist feature placement technique that enhances the resulting depth of focus even when imaging features have dimensions on the order of a quarter of the wavelength of the imaging system.