A　hybrid　phase　retrieval　approach　is　proposed　to　address　the　twin　image　problem　in　the　reconstruction　of　in-line　digital　holograms.　The　approach　is　a　variant　iterative　transform　algorithm　and　exploits　two　mostly　natural　constraints　of　a　sample,　namely,　the　finite　transmission　and　the　finite　support.　Here,　the　initial　sample　support　estimate　is　first　refined　by　applying　the　finite　transmission　constraint　with　phase　flipping.　The　approach　provides　better　reconstruction　than　if　only　the　finite　transmission　constraint　is　used　and　improve　the　convergence　rate　of　Fienup＇s　algorithm　owing　to　a　better　estimate　of　support　especially　for　strong　samples　with　complex　structures.　Both　simulation　and　experimental　results　are　presented.　(C)　2011　Society　of　Photo-Optical　Instrumentation　Engineers　(SPIE).　[DOI:　10.1117/1.3596203]