REMOVAL OF RELATIVELY UNIMPORTANT SHAPES FROM A SET OF SHAPES

A method for reducing a number of shapes, and a computer readable program code adapted to perform said method. The method forms first and second shape patterns. The second shape pattern includes the first shape pattern and error shapes. The error shapes are extracted from the second shape pattern. At least one environment shape corresponding to each error shape is derived from a subset of the error shapes. For example, each error shape in the subset may be expanded to form a corresponding expanded shape, and at least one environment shape corresponding to each expanded shape may be formed by removing all portions of the expanded shape common to the second shape pattern. The environment shape reflects a local geometric environment of its corresponding error shape. A subset of the environment shapes are deleted such that only unique environment shapes satisfying a selection criterion remain.