//这个是javascript 实现网页图片等比例缩放
function DrawImage(ImgD,imgwidth,imgheight){   
         var image=new Image();   
         image.src=ImgD.src;   
         if(image.width>0 && image.height>0 ){
		 	var rate = (imgwidth/image.width < imgheight/image.height) ? imgwidth/image.width:imgheight/image.height; 
		 	if(image.height<image.width){   
					   if(rate <= 1){   
						 //ImgD.width = image.width*rate;   
						 ImgD.height = imgheight;
						 //image.height*rate;   
					   } else {   
						 ImgD.width = image.width;   
						 ImgD.height =image.height;   
					   } 
		    }
         	else{
		     if(rate <= 1){   
             ImgD.width = imgwidth;
			 //image.width*rate;   
             //ImgD.height = image.height*rate;   
           } else {   
             ImgD.width = image.width;   
             ImgD.height =image.height;   
           }
		   }   
       }
	   }