var flag=false; 
function DrawImage_WH(ImgD,sw,sh){
var image=new Image();
var iwidth = sw; //定义允许图片宽度
var iheight = sh; //定义允许图片高度
image.src=ImgD.src;
if(image.width>0 && image.height>0){
   flag=true;
   if(image.width/image.height>= iwidth/iheight){
      if(image.width>iwidth){ 
         ImgD.width=iwidth;
         ImgD.height=(image.height*iwidth)/image.width;
      }else{
         ImgD.width=image.width; 
         ImgD.height=image.height;
      }
      ImgD.alt=image.width+"×"+image.height;
   }
   else{
      if(image.height>iheight){ 
        ImgD.height=iheight;
        ImgD.width=(image.width*iheight)/image.height; 
      }else{
        ImgD.width=image.width; 
        ImgD.height=image.height;
      }
      ImgD.alt=image.width+"×"+image.height;
  }
}
}