Abstract: A printing system for printing on a substantially planar surface of a 3D-object includes a printer for printing on the planar surface of the 3D-object and a controller configured to control printing of the printer. The printing system further includes a mask generation module configured to generate a mask having the shape of the planar surface from a 3D-model of the 3D-object and to provide the controller with the mask to prevent printing outside the planar surface according to the mask.