Transparency lost

[Nicolas Ferré]

When inserting a png image without background in it, I lost the 
transparency if I compile the document with pdflatex (I need it because 
I work on a beamer presentation).
Any solution to keep the transparency ?

--
 Dr. Nicolas Ferre'
 Laboratoire de Chimie Theorique et de Modelisation Moleculaire
 UMR 6517 - CNRS Universite' de Provence
 Case 521 - Faculte' de Saint-Jerome
 Av. Esc. Normandie Niemen
 13397 MARSEILLE Cedex 20 (FRANCE)
 Tel : (+33)4.91.28.27.33              Fax : (+33)4.91.28.87.58
 Please avoid sending me Word or PowerPoint attachments.
 See http://www.gnu.org/philosophy/no-word-attachments.html