18. The encoder claimed in claim 17 , wherein the new probability set is a subset of the predefined probability set.
18. The encoder claimed in claim 17 , wherein the new probability set is a subset of the predefined probability set. 19. The encoder claimed in claim 18 , wherein the processor is configured to define the mapping by determining, for each probability of the predefined probability set, to which one of the probabilities from the new probability set it is mapped on the basis of minimizing a relative entropy expression.