1. A lithographic apparatus, comprising: an array of individually controllable elements that modulate a beam of radiation; a compressed pattern memory that stores a compressed representation of a requested dose pattern to be formed on a substrate by the modulated beam; and a dictionary decompressor that at least partially decompress the compressed representation, wherein the dictionary decompressor comprises, a first dictionary memory, and a first dictionary decoder that at least partially decompresses at least a part of the compressed representation by extracting, from the first dictionary memory, portions of pattern data corresponding to references to the first dictionary memory contained in the compressed representation.