A method generates an image from a set of image zones each delimited by a contour of polygonal shape defined by a set of vertexes, and comprising pixels having an attribute value which can be deduced from the value of a corresponding attribute of each of the vertexes of the image zone. The piston is cast with no coring and thus includes no aperture in the as-cast piston for a wrist pin. Integral interior magnets also apply magnetic therapy to the foot within each shoe.