1. Wavelet transform method of compressing digital image data, comprising a step of transforming digital image data into wavelet coefficients divided into sub-bands, a step of quantifying said wavelet coefficients, and a step of entropically coding said quantified wavelet coefficients, characterized in that it comprises, between the transformation and quantifying steps, a step of estimating, for each coefficient of each sub-band of the image, first and second sets of prediction parameters respectively associated with “North-South” and “West-East” directions as a function of the values of the wavelet coefficients of its North and West neighbors, and, in the entropic coding step, there is determined for each coefficient of each sub-band of the image a prediction of the esperance and the width of a Laplace type function representing its probability density as a function of said first and/or second sets of prediction parameters and the quantified wavelet coefficients of its North neighbor or its West neighbor and said quantified wavelet coefficients are coded entropically using the associated esperances and widths determined in this way.