The invention concerns a method of inserting a suppementary information item in a set of data reprenting physical quantities, the data having been processed by the steps of, a) partitioning (E2) the set into subsets, b) entropic coding (E4) of each of the subsets, c) selecting (E8), for each of the subsets, a compression rate and distortion pair according to a global compression rate or a global distortion, d) writing, for each of the subsets, an index (T.sub.ij) representing the selected compression rate and distortion pair, in a file containing the coded subsets, characterised in that it also includes a step (E11) of modifying the selected compression rate and distortion pairs, according to the supplementary information (w.sub.m).