A method for converting a vector-based representation of a desired device pattern for an exposure apparatus, a lithography or exposure apparatus, an apparatus and method to provide data to a programmable patterning device, and a device manufacturing method. In an embodiment, the method for converting outputs a rasterized representation of the desired dose pattern of radiation corresponding to the desired device pattern, wherein the vector-based representation includes primitive data identifying one or more primitive patterns; and instance data identifying how at least a portion of the desired device pattern is formed from one or more instances of each identified primitive pattern, the method including forming a rasterized primitive of each primitive pattern identified in the primitive data, and forming the rasterized representation by storing each rasterized primitive in association with the instance data corresponding to that rasterized primitive.