Memory addresses for a data stream are generated by a stream parameter generator that calculates a set of stream parameters for each of a number of memory access patterns and a regional address generator that calculates a sequence of addresses of a memory access pattern from a corresponding set of stream parameters. The stream parameters, which may include START_ADDRESS, STRIDE, SKIP and SPAN values for example, are updated in accordance with an update( ) function. The update( ) function, which may be defined by a user, defines how stream parameters change from one memory access pattern to the next. In one application, the update( ) function describes how the position, shape and/or size of a region of interest in an image changes or is expected to change.