function imgvan(mw,mh,img)
{
 var wr,hr,width,height;
 width=img.width;
 height=img.height;
 if(width<=mw&&height<=mh) return;
 if(width<=mw&&height>mh) {img.height=mh;return;}
 if(width>mw&&height<=mh) {img.width=mw;return;}
 wr=mw/width;
 hr=mh/height;
 if(wr<hr)
 {
  img.width=mw;
  img.height=wr*height;
 }
 else
 {
  img.height=mh;
  img.width=hr*width;
 }
}