1. A method of producing a hierarchical auxiliary map for a sample of a signal encoded at multiple different levels of quality in a hierarchy, the method comprising: selecting an element from a rendition of the auxiliary map at a first level of quality; generating a plurality of sub-elements by applying one or more filtering operations to (i) the element and (ii) one or more elements which are neighbors of said element; and generating a rendition of the auxiliary map at the second level of quality by using the generated plurality of sub-elements.