1. A process for preparing a photolithography mask usable in the fabrication of a semiconductor device for printing isolated and dense design features onto a photosensitive layer formed over a substrate, comprising: providing a proposed mask layout having a set of main features corresponding to the design features and a set of sub-resolution assist features (SRAFs) added to correct iso-dense bias in the printing of the main features; checking the proposed mask layout to determine if the set of SRAFs have been positioned properly to correct the iso-dense bias, including: dividing each edge of each main feature in the set of main features into a set of sections; forming a set of segments by searching away from each one of the set of sections over a threshold distance perpendicular to the edge, to determine if any portion of a main or sub-resolution assist feature is located within the threshold distance, wherein the threshold distance is a given maximum permissible distance to a single centered shared SRAF shared by the main feature and another main feature in the set of main features; flagging each segment that does not include any portion of a main or sub-resolution assist feature located within the threshold distance; storing segment data comprising the set of flagged segments for each main feature in the set of main features; and classifying each main feature and assigning a pass/fail level based on the number of flagged segments; and revising the mask layout by automatically rearranging the sub-resolution assist features based on the assigned pass/fail levels.