function sistemaRes(chiave,height,width){
var img1=document.getElementById(chiave);
var coeff=img1.width/img1.height;
if (coeff < width/height){
	if (img1.height > height ) {	
		img1.height= height;
		img1.width=coeff*height;
		}
}
else
{
	if (img1.width > width) 
	{
		img1.width= width;
		img1.height= width/coeff;
	}
}
}