按比例缩放图片的js代码

 <script language="JavaScript" type="text/javascript"> 
  function DrawImage(ImgD,FitWidth,FitHeight){    
   var image=new Image();
   image.src=ImgD.src;   
   if(image.width>0 && image.height>0){    
    if(image.width/image.height>= FitWidth/FitHeight){       
     if(image.width>FitWidth){              
      ImgD.width=FitWidth;              
      ImgD.height=(image.height*FitWidth)/image.width;         
     }else{               
     ImgD.width=image.width;               
      ImgD.height=image.height;           
     }        
    } else{  
     if(image.height>FitHeight){      
     ImgD.height=FitHeight;               
     ImgD.width=(image.width*FitHeight)/image.height;   
     }else{              
     ImgD.width=image.width;              
     ImgD.height=image.height;          
     }        
   }     
   } 
  }
</script> 
按比例显示的调用：<img src="show_image.jsp?id=<%=request.getSession().getAttribute("id")%>" width="70px" height="70px" onload="javaScript:DrawImage(this,70,70);"><br>