function DrawImage(ImgD,iwidth,iheight)
    {   
    //参数(图片,允许的宽度,允许的高度)   
    var image=new Image();   
    image.src=ImgD.src;
    if (image.width > 0 && image.height > 0)
    {   
      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;   
          }
      }
      else{   
          if(image.height>iheight){     
              ImgD.height=iheight;   
              ImgD.width=(image.width*iheight)/image.height;           
          }else{   
              ImgD.width=image.width;     
              ImgD.height=image.height;   
          }   
        }   
      }   
    }