  In the context of assessing and characterizing structures in X-ray images, we
compare different approaches. Most often the intensity level is very low and
necessitates a special treatment of Poisson statistics. The method based on
wavelet function histogram is shown to be the most reliable one. We also
present a multi-resolution filtering method based on the wavelet coefficients
detection. Comparative results are presented by means of a simulated cluster of
galaxies.
