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;    
                  }    
              }    
            }    
   }