Image Javascript onLoad

Pourquoi le onLoad de ne pas se déclencher?

      function FULL_IMAGE(fimage){
document.getElementById("FULL_SRC").onLoad = function(){
offsetTop = document.getElementById("FULL_SRC").height / 2;
offsetLeft = document.getElementById("FULL_SRC").width / 2;
document.getElementById("FULL_SRC").style.marginTop="-"+offsetTop+"px";
document.getElementById("FULL_SRC").style.marginLeft="-"+offsetLeft+"px";
}
document.getElementById("FULL_SRC").src=fimage;
document.getElementById("FULL_VIEW").style.display="block";
}

source d'informationauteur Shane Larson