//图片按比例缩放
var flag=false;
function DrawImage(ImgD,ImgWidth,ImgHeight){
	var image=new Image();
	var iwidth=ImgWidth;           //定义允许图片宽度
	var iheight=ImgHeight;           //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;
	  }
	}
}
//调用：<img src="图片" onload="javascript:DrawImage(this,131,100)">