OPC is sometimes applied to a pattern to generate a mask that will generate a better image. OPC may be as simple as biasing line widths or as complicated as adding assist features such as serifs or scatter bars.
PanOPC allows EM-Suite users with the Gazillion option to run OPC on GDS layouts. In addition to basic operations such as corner rounding and biasing, an iterative algorithm is also supported which can perturb the mask either in a continuous or with Manhattenized features to optimize the result. The iterative algorithm supports using the full simulation pipeline for evaluating the results at each iteration.
PanOPC is suitable for small areas only such as bit-cell optimization and not intended for full chip OPC.