1. Method of inserting supplementary information in a set of data representing physical quantities, the data having been processed by the steps of: partitioning (E 2 ) the set into subsets, entropic coding (E 4 ) of each of the subsets, selecting (E 8 ), for each of the subsets, a compression rate and distortion pair according to a global compression rate or a global distortion, writing, for each of the subsets, an index (T ij ) representing the selected compression rate and distortion pair, in a file containing the coded subsets, characterised in that it also includes a step (E 11 ) of modifying the selected compression rate and distortion pairs, according to the supplementary information (w m ).