1. A method of operating a computer to produce an object-based description of an embroidery pattern subject, from a subject bitmap describing the subject, the method comprising the steps of: analysing the subject bitmap to identify a skeleton of the subject; analysing the skeleton to identify a plurality of nodes interlinked by a plurality of paths; traversing the skeleton by following the paths and nodes; and during the traversal, generating a series of objects describing the subject for the object-based description.