1. A method of inspecting a photolithographic mask, comprising: receiving a first design database; receiving a bias factor specifying an adjustment to a feature of the first design database; adjusting, by a computing device, the feature of the first design database according to the bias factor to produce a first biased design database; performing, by an image rendering system, image rendering on the first biased design database to produce a first database image; receiving a first mask image of a physical mask created based on the first design database; comparing the first database image with the first mask image; and determining a new value for the bias factor based on the comparison.