1. For use with a laser or other pattern generator in which plural beams are swept across successive blocks of a target to form an image, a data handling system comprising: preprocessor means for providing a set of vectors defining edges of polygons to be included in the image formed in said successive blocks, a bit map precursor memory having a set of storage locations corresponding to each of said beams, a pipeline comprising plural beam processors each associated with a respective beam and arranged in series to successively process vectors from said preprocessor means, each beam processor having means for determining if the processed vector defines an edge which is intersected by the beam to which that beam processor is associated, and if so, for entering into said precursor memory, at a storage location corresponding to such intersection, a beam on/off direction control signal established by said vector, and means for modulating said plural beams, as they are swept, with information derived from the resultant contents of said bit map precursor memory.