The method comprising a wavelet-based spatial analysis step comprising filtering operations of the picture at the high resolution format and horizontal and/or vertical decimation operations of the filtered picture to supply subband signals, is wherein a decimation operation is carried out according to a factor different from an even value and corresponds to the quotient of the horizontal and vertical dimensions of the first and second format such that the low frequency picture thus obtained relative to the low frequency subband signals, corresponds to the second format.